Every audit we run includes an eighteen month fee reconciliation. It is the least interesting part of the work and it has never once come back clean.
Wrong dimensions
Amazon measures your product when it arrives and bills the size tier it measured. If that measurement is wrong, and it often is by a few millimetres on something sitting right on a tier boundary, you pay the higher rate on every unit until somebody notices.
One pet brand we audited had been paying large standard rates on an item that measured into standard. The difference was seventy four cents a unit across about nine hundred units a month, running since 2023. Nobody had checked because the fee looked plausible and there is no alert for being quietly overcharged.
Check it yourself: pull the FBA fee preview report, compare the dimensions Amazon holds against your own measurements of the packaged unit, and open a case for anything near a boundary. Measure the box you actually ship, not the product.
Inventory that never arrived
Units go missing inbound. Units get damaged in the warehouse. Units get refunded to a customer who never returned them. Amazon reimburses for all of it, and increasingly does so automatically, but automatic does not mean complete.
The reports you want are Inventory Adjustments, Reimbursements, and Returns, pulled across eighteen months, reconciled against each other. What you are looking for is any adjustment with a lost or damaged reason code that has no matching reimbursement line. Then you file, one case per discrepancy, with the shipment ID and the numbers.
Expect this to take a day and to find between one and three percent of your fulfilment costs. The pet brand got $9,400 back over eleven weeks.
Storage on things you should have written off
This one is not an error, it is a decision nobody made. Aged inventory accrues long term storage fees on a schedule most sellers never look at, and the product accruing them is by definition the product nobody is buying.
Sort your inventory age report by units over 271 days. For each line the question is simple: will this sell through before the next long term fee lands? If not, liquidate, remove, or run an aggressive clearance. Holding it costs money every month and holding it is rarely the cheaper option.
The pattern
None of these are sophisticated. They persist because everybody assumes the platform is keeping score correctly on their behalf, and mostly it is, except in the places where it is not and nobody is looking. Put an hour in the calendar every month. It pays better per hour than almost anything else you could be doing.
