When a supplier changes a cost, recheck every SKU's margin before it leaks
Updated · By Ecomsellertool editorial team
To catch supplier cost changes, treat every new price list, invoice line that differs from the PO, and freight or duty change as an event. Rules recompute landed cost and contribution margin per SKU on each channel after its fees, flag SKUs below your margin floor, and queue proposed fixes, such as repricer minimums, channel prices, ad targets and reorders, for a person to approve.
- Amazon's referral fee is a percentage of the total price or a minimum, whichever is greater; Home and Kitchen is 15% with a $0.30 minimum (checked October 29, 2026).
- Amazon FBA, US, Large standard-size, 1 to 1.25 lb, priced $10 to $50: $5.04 non-peak and $5.34 at peak (Oct 15, 2026 to Jan 14, 2027), plus a 3.5% surcharge.
- Walmart Marketplace referral fees are a percentage of the total sales price, which includes shipping, handling and gift wrap; Home, Kitchen, Decor and Garden is 15% (checked October 29, 2026).
- Walmart lists zero setup or monthly fees for Marketplace; Amazon's Professional plan is $39.99 a month plus selling fees (checked October 29, 2026).
- In this recipe fixed rules do every calculation; an AI model only reads supplier price lists and invoices, and a person approves every price, bid and reorder change.
The step map: who runs each step
Trigger: A new supplier price list or quote, a supplier invoice line whose unit cost differs from the PO, or a change to a freight, duty or currency rate that feeds landed cost.
| Step | What happens | Who runs it |
|---|---|---|
| 1 | The cost change is captured: a price list or quote arrives by email or portal, an invoice line fails the PO price check, or a freight, duty or exchange rate is updated in the cost table. | Rule |
| 2 | An AI model reads price lists and invoices that arrive as PDFs or spreadsheets, extracts supplier SKU, unit cost, currency and effective date, and maps each supplier SKU to your SKUs. Lines it cannot map with confidence go to a person. | AI model |
| 3 | Rules classify the change with the rule table, find every affected SKU, including bundles and kits that contain it, and recompute landed cost from unit cost, freight, duty and other inbound costs. | Rule |
| 4 | For each SKU and channel, rules subtract that channel's fees, outbound shipping and ad cost per unit from the current price, compare contribution margin with the floor, and work out the lowest price that meets the floor. | Rule |
| 5 | The workflow drafts proposed changes for SKUs below the floor: a new repricer minimum, new prices on Shopify, Amazon and Walmart, a lower target ACOS for ads, and a flag on the next reorder. | Rule |
| 6 | A person reviews each proposal with the old and new cost, the margin on every channel and the price needed to hold the floor, then approves, edits or rejects it, or goes back to the supplier. | Person |
| 7 | Approved changes are written to the repricer, the channels and the ad rules; the new cost is saved with its effective date, and every change is logged with who approved it. | Rule |
5 rule steps · 1 AI model step · 1 person step. A rule follows fixed logic you approve; an AI model handles messy input and its output is checked by rules; a person makes the calls listed below.
What stays with a person
- Which cost is right when the invoice and the PO disagree
- Every price change, repricer minimum and ad target the workflow proposes
- Whether to absorb a cost increase, raise prices, renegotiate or change supplier
- Duty and tariff rates and freight allocation rules, with your customs broker and accountant
- The margin floor itself, per channel and per product line
Which tools can run it
- A cost spreadsheet with margin formulas per channel, updated by hand, for a few suppliers and under a hundred SKUs
- Zapier, Make or n8n with an AI model step that reads supplier price lists into the sheet and posts alerts to Slack
- Custom code on your accounts, for many suppliers, landed cost per shipment, bundles, three or more channels and write-back
Systems it connects
- Supplier price lists, quotes and invoices (email or portal)
- Purchase orders (ERP, inventory system or Shopify)
- Cost table with freight, duty and currency rates
- Amazon Seller Central and Amazon Ads
- Walmart Seller Center
- Shopify
- Repricer
- Slack or email for approvals
Build size: Medium
The math is simple; the work is mapping supplier SKUs, allocating freight and duty per unit, and getting each channel's fees right per SKU.
A supplier raises a unit cost by 20 cents. The new price list sits in an inbox, the invoice gets paid, and the repricer keeps selling at a minimum set against last year's cost. Nobody notices until the month's profit report, weeks later, on every unit sold since. This recipe turns each cost change into an event: recompute the landed cost, recheck margin on every channel after its own fees, and put a short list of proposed fixes in front of a person. It is one page of our automation library.
Two neighbors do different jobs. Our wholesale price list sync covers the prices you charge wholesale buyers; this page covers what you pay. Our supplier invoices to QuickBooks and Xero bills recipe covers booking the bill; this page uses the same invoice to check margin.
How do you work out landed cost and the price that holds your margin floor?
Three formulas, in order. Build them in a sheet today, even before anything is automated.
Landed cost per unit = supplier unit cost + inbound freight per unit + duty per unit + other inbound costs per unit
Contribution margin per unit = price − referral fee − fulfillment or shipping cost − payment fee − ad cost per unit − landed cost
Floor price = (landed cost + fulfillment or shipping cost + ad cost per unit) ÷ (1 − referral fee rate − margin floor)
Duty is usually a rate on the customs value, and freight must be spread across a shipment by weight, volume or value. Those choices belong to your customs broker and accountant; this is not tax or customs advice. The floor is your own number: the contribution margin, after ads, below which a sale is not worth making. If the floor price lands in a different fee band, recompute with that band's fee.
An illustrative example, not a client result. A kitchen item weighs just over 1 lb in its box. The supplier's new price list moves the unit cost from $6.00 to $7.20. Inbound freight is $0.90 a unit, duty is an assumed 10% of unit cost, and prep is $0.30. Landed cost goes from $7.80 to $9.12. The margin floor is 28% of price.
| Channel (illustrative) | Price | Channel fees per unit | Shipping and ads per unit | Margin at $7.80 cost | Margin at $9.12 cost | Floor price at new cost |
|---|---|---|---|---|---|---|
| Amazon FBA | $29.99 | Referral 15%: $4.50; FBA peak fee with surcharge: $5.53 | Ads $3.00 | $9.16 (30.5%) | $7.84 (26.1%), below floor | $30.97 |
| Walmart, seller-fulfilled | $29.99 | Referral 15%: $4.50 | Shipping $6.50; ads $1.50 | $9.69 (32.3%) | $8.37 (27.9%), below floor | $30.04 |
| Shopify | $32.99 | Payment fee placeholder 3% + $0.30: $1.29 | Shipping $6.50; ads $4.00 | $13.40 (40.6%) | $12.08 (36.6%), above floor | No change needed |
One cost change, three answers. On Amazon, the item needs about $1 more in price, or $0.56 less ad spend per unit, which means a target ACOS near 8.1% instead of 10%. On Walmart, it misses the floor by a few cents, so a person may choose to absorb it. On Shopify, nothing moves. The Shopify fee is a placeholder: replace it with the card rate on your own plan.
Which fees sit between price and margin on each channel?
These are the fees the formula subtracts. Each figure was read on the platform's own page on October 29, 2026. Fees change, so the workflow reads them per SKU from each channel's own fee data rather than from a table like this one.
| Channel | Fee | What we read on the platform's page |
|---|---|---|
| Amazon | Referral fee | Amazon's selling pricing page says you pay a percentage of the total price or a minimum amount, whichever is greater, with rates from 3% to 45% by category. Home and Kitchen is 15% with a $0.30 minimum (checked October 29, 2026) |
| Amazon | FBA fulfillment fee | Amazon's 2026 US FBA fee page lists $5.04 for a Large standard-size unit of 1 to 1.25 lb priced $10 to $50 from January 15 to October 14, 2026, and $5.34 at peak from October 15, 2026 to January 14, 2027. A 3.5% fuel and logistics surcharge applies on top from April 17, 2026 (checked October 29, 2026) |
| Amazon | Selling plan | The Professional plan is $39.99 a month plus selling fees; spread it across units only if you want it inside the margin |
| Walmart | Referral fee | Walmart's referral fee page says the percentage applies to the total sales price, including shipping and handling, gift wrap and other charges. Home, Kitchen, Decor and Garden is 15%, and Walmart lists zero setup or monthly fees (checked October 29, 2026) |
| Shopify | Payment fee | Depends on your plan and payment provider. We could not read a US Shopify Payments card rate on Shopify's public pages on October 29, 2026, so none is quoted here; use the rate on your own plan |
Two details catch teams out. Walmart charges its referral fee on shipping you collect, so a shipping charge raises the fee. And Amazon's fulfillment fee depends on the price band, so a price change that crosses $10 or $50 changes the fee, which is why the floor price is checked against its band.
What does the workflow do for each kind of cost change, and who approves?
Each kind of change has its own trigger, its own action and its own approver. This table is the second half of the build.
| Cost change | What the workflow does | Who approves |
|---|---|---|
| New supplier price list or quote with an effective date | Maps each line to your SKUs, recomputes landed cost from the effective date, flags SKUs below the floor and drafts price, repricer and ad changes | Purchasing confirms the new costs; the pricing owner approves the changes |
| Invoice unit cost differs from the PO | Holds the line, recomputes margin at the invoice cost so the size of the hit is visible, and passes the hold to the bills workflow | Purchasing decides which price is right with the supplier before any cost is updated |
| Freight rate change | Re-spreads freight per unit by your allocation rule across open and incoming POs, then recomputes landed cost | Operations lead, using the rule agreed with your accountant |
| Duty or tariff rate change | Recomputes duty on the customs value for the affected products and flags SKUs below the floor | Finance, with your customs broker confirming the rate (not tax advice) |
| Currency move on a non-USD supplier | Recomputes cost at the new rate once the move passes your threshold | Finance |
| Cost decrease | Updates the cost and reports the margin gained; proposes no price cut on its own | Pricing owner, if they want to pass it on |
| Change below your noise threshold | Updates the cost record and logs it; no alert | Nobody; it appears in the weekly log |
The proposals go to one queue. For a SKU below the floor, a person sees the old and new landed cost, margin per channel, the floor price, and four drafted options: a new repricer minimum, new channel prices, a lower ad target and a flag on the next reorder. A reorder flag matters when the cost change has not reached your shelf yet. It is the moment to negotiate, buy a smaller quantity, or change supplier before the new cost is locked in.
Where does the cost data come from?
Supplier price lists arrive as PDFs, spreadsheets or portal exports, each in its own layout. This is the one step where an AI model helps: it reads the document, extracts supplier SKU, cost, currency and effective date, and maps lines to your SKUs. It never changes a cost on its own. Lines it cannot match go to a person, and the mapping it learns is saved so the next list is faster.
Invoice differences come from the same matching our supplier invoices recipe runs: when a unit cost is above the PO, that recipe holds the bill and this one shows what the difference does to margin. Freight and duty come from your forwarder's and broker's invoices, and the per-unit split follows your accountant's rule. Fees come from each channel. Ad cost per unit comes from your ad reports, divided by units sold over the same period.
How does it fit with pricing and ad rules?
A repricer minimum is a margin decision written as a price. When cost rises, the minimum must rise with it, or the repricer will happily match a competitor below what the product now costs to sell. The same is true for MAP: our MAP price monitoring recipe watches advertised prices against a floor, and a cost change may move that floor too.
Ads need the same update. Break-even ACOS is the margin before ad spend divided by price; when landed cost rises, it falls, and a bid rule tuned to the old number keeps buying sales at a loss. Our glossary entry on margin ACoS explains the ratio, and contribution margin explains the base. Reorders close the loop: our low-stock alerts and draft purchase orders recipe can carry the margin flag into the next draft PO.
Which tool should run it?
| Level | Fits when | What to watch |
|---|---|---|
| A cost spreadsheet with margin formulas per channel | A few suppliers, under a hundred SKUs, costs that change a few times a year | Someone must remember to update it when a price list arrives; fees go stale |
| Zapier, Make or n8n with an AI model step | Price lists by email, one or two channels, alerts to Slack | Supplier SKU mapping and bundles get messy; log every run |
| Custom code on your accounts | Several suppliers, freight and duty per shipment, bundles, three or more channels, write-back to repricer and ads | Can run on Ecomsellertool Growth OS beside your inventory and ad data |
If you are weighing the workflow tools, our Zapier vs Make vs n8n comparison covers how each counts work. Ad spend tied to stock and margin is covered from the Amazon side in our inventory-aware ad spend page.
Who builds supplier cost change alerts?
Ecomsellertool builds workflow automation on your own accounts and systems; we have built software on Amazon's seller APIs since 2017. For cost change alerts we agree your landed cost formula, fee sources and margin floors first, then connect price lists, invoices, the approval queue and write-back. Send a project brief below, or read how our workflow automation service works.
The building blocks are work we have shipped:
- COGS per product, updated over time. For Beezboard we built cost management that maps COGS to products, with new costs added on a monthly or annual frequency, and a profit and loss statement per marketplace from Amazon's finance data.
- Repricing rules with a price boundary. For a client's custom Amazon repricer we built reprice rules against the Buy Box or the lowest price, with options to stay above a set price.
- Net margin per brand and product type. For Lavley we built sales analytics that bring advertising cost into profit, and goals set on units, revenue, net profit and net margin.
Get your cost change alerts built
Send us your suppliers, channels and margin floor
Describe the workflow you want automated. We reply with a written plan: scope, timeline and a fixed price.
Frequently asked questions
How do I know which SKUs are affected when a supplier raises prices?
Map every supplier SKU to your own SKUs once, including bundles and kits that contain the item. When a new price list arrives, the workflow compares each line with the cost on file and lists every one of your SKUs whose landed cost moved, with the size of the change.
What is landed cost for an ecommerce product?
Landed cost is what one unit costs by the time it is ready to sell: the supplier's unit cost plus inbound freight, duty and other inbound costs such as inspection or prep, spread per unit. How you allocate freight and duty across a shipment is a choice to make with your accountant.
How do I calculate the minimum price to keep a margin floor?
Take the fixed costs per unit, which are landed cost, fulfillment or shipping and ad cost, and divide them by one minus the referral fee rate minus the margin floor. For a 15% referral fee and a 28% floor, divide by 0.57. Check that the new price stays in the same fee band.
Should a repricer's minimum price change when my costs change?
Yes. A repricer minimum set from an old cost can let the price fall below what the product now costs to sell. The workflow proposes a new minimum from the recomputed floor price, and a person approves it before it is written.
Should prices go up automatically when a supplier cost goes up?
Not in this recipe. Price is a commercial decision: you may absorb a small increase, raise the price on one channel only, cut ad spend, or push back on the supplier. The workflow does the math and drafts the options; a person picks one.
How is this different from wholesale price list sync?
Wholesale price list sync is about the prices you charge wholesale buyers. This recipe is about what you pay: when a supplier, freight or duty cost changes, it rechecks your margin on every selling channel and proposes changes for approval.
