What the measurement caught
Findings from our own Amazon account, each with the date it was measured. Two of them are our own mistakes, which is the point: a tool that has never been wrong in public has either never checked or is not telling you.
Not included anywhere on this page: what we pay our supplier, or anything you could derive it from. The fees below are Amazon's numbers about our account. What we paid for the goods is not.
A referral rate that more than doubled, mid-month
What is usually assumed: Most tools take the referral fee as a fixed category percentage and multiply. It is the one input everybody treats as a constant, because Amazon publishes it as one.
What we measured: Splitting the same settlement table by posting date shows two different regimes on the same product, on the same account, weeks apart.
| Period | Orders | Units | Referral | Per unit |
|---|---|---|---|---|
| Before 15 Jul 2026 | 75 | 103 | 5.63% | $1.93 |
| From 15 Jul 2026 | 95 | 119 | 12.61% | $4.41 |
Why it costs money: Break-even ACoS moved from 39.1% to 35.2%. Every bid, coupon and price decision made against the old figure was made against a number that had already stopped being true — and nothing in an advertising dashboard reports it, because the deduction does not happen there.
Measured 2026-08-18 · 222 units across 170 settled orders, amazon.com.au
The fee estimate is not what the settlement charges
What is usually assumed: Amazon publishes a fee estimate per ASIN, and a profit tool that reads it looks like it is reading Amazon's own number.
What we measured: On our own product the FBA fee the settlement deducted was $10.85 against a $10.16 estimate — and on amazon.com.au every fee carries 10% GST that the estimate excludes entirely.
Why it costs money: A break-even built on estimates read $18.94 when the settled number was $20.17. That gap is wider than the margin most sellers are optimising toward, which means the optimisation was pointed at the wrong target the whole time.
Measured 2026-08-05 · 30-day settlement window, 88 units, amazon.com.au
We got our own number wrong. Twice.
What is usually assumed: That a tool built by people who measure things carefully gets the measurement right the first time.
What we measured: Our published break-even went $18.94 → $20.17 → $20.88 across three corrections. The first came from the settlement backfill, the second from consumption tax on fees, the third from the referral shift above.
Why it costs money: The reason to say this out loud rather than quietly restate the latest figure: a tool that has never been wrong in public has either never checked or is not telling you. Ours reports the correction because the correction is the product working.
Measured 2026-08-18 · internal measurement history, amazon.com.au
The bug that manufactures a plausible wrong answer
What is usually assumed: That reading settlement line items is simply better, and getting it right is a matter of having the data.
What we measured: Filtering settlement rows on the description alone matches both the item-price row and the negative promotion row. That double-counts units, shrinks the revenue denominator, and produces a confident blended rate of about 9.6% that is not any rate the account was ever charged.
Why it costs money: It also manufactured a phantom defect — dozens of orders appearing to disagree about quantity. The fix is to filter on the amount type and the description together; with that done, item-price units equal fee units on every settled order. We publish this because anyone building the same thing will hit it, and because a number being specific is not evidence that it is right.
Measured 2026-08-18 · settlement line-item reconciliation, amazon.com.au
The limitation of this page
Nothing here updates itself. The engine detects an unstable referral rate on a rolling window and warns a connected seller in real time, but no table records the event — so a shift that has scrolled out of the window cannot be recovered later. Persisting those detections is the next piece of work. Until then these are case studies, not a feed, and saying so is cheaper than being caught pretending otherwise.