The most expensive mistake Amazon sellers make is treating Amazon’s two-week disbursement as their revenue. That deposit isn’t your sales total. It’s what’s left after Amazon takes referral fees, FBA fees, storage fees, advertising costs, and any refunds or chargebacks. If you’re booking that disbursement amount as revenue, your books are wrong from the start and your profit margins are fictional.

Not tracking inventory costs properly is the second major issue. You can’t calculate true profit without knowing what you paid for the products you sold. Cost of goods sold should match the units sold in each period, not just when you bought inventory. Running on a cash basis where you expense inventory when you buy it rather than when you sell it gives you wildly inaccurate profit numbers. This is especially problematic during Q4 when you’re stocking up for holiday sales but haven’t sold the product yet.

Ignoring the Amazon fee breakdown hurts decision-making. Amazon charges referral fees, fulfillment fees, storage fees, advertising fees, and various other charges. Each one affects margin differently. If you’re not tracking these separately in your e-commerce bookkeeping, you can’t identify which fees are eating into profit or whether a product is actually worth selling after all costs.

Reconciliation problems happen when sellers don’t match Amazon settlement reports to their actual transactions. Amazon’s reports are confusing. They include adjustments, reimbursements, and timing differences that don’t match a simple revenue minus fees calculation. Most sellers just book the deposit and move on, which leaves money and accuracy on the table.

Multi-state sales tax is a compliance landmine many sellers ignore. Storing inventory in Amazon’s FBA warehouses creates nexus in those states, meaning you likely owe sales tax in places you’ve never set foot in. Amazon collects and remits in most states now, but the rules vary and the liability still falls on you if something goes wrong.

The final common mistake is mixing personal and business finances. Using one credit card for inventory purchases and personal expenses makes it nearly impossible to track actual business costs. Open a separate business account and run everything through it.

These mistakes compound over time. Bad data for one month becomes bad data for twelve months, and by tax time you’re either overpaying because you can’t prove your deductions or underpaying because you didn’t realize you owed more. A Scottsdale bookkeeper who understands Amazon’s fee structure and inventory timing can set up your books correctly from the start. That saves money and stress compared to cleaning up a mess later.