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Merge Amazon Seller Central and Mercari Sales Data for Cost of Goods Sold Tracking

Calculating cost of goods sold across channels requires item-level data lined up the same way regardless of where it sold.

Why Amazon Seller Central and Mercari exports don't line up

Amazon Seller Central: a purchase date/time column stamped in UTC, not your local time; item price, promotion discounts, and Amazon referral fees split across several columns; an Amazon Order ID in a long dashed format (e.g. 123-4567890-1234567). Also, reports differ noticeably between the 'All Orders' report and the Payments/Settlement report — totals rarely match at a glance.
Mercari: a sold date in the seller's local time; item price and Mercari's selling fee shown separately, with shipping often bundled into the price; an order ID tied to a single sold item. Also, like other reseller apps, the export is minimal with no tax breakdown and mixes cancelled orders into the same file.

For cost of goods sold tracking, that mismatch is exactly what causes hours of manual cleanup every period.

Open CSV Experts and set your target columns once (Date, Channel, Order ID, Total).
Drop in your Amazon Seller Central export and map its columns once.
Drop in your Mercari export and map it the same way — both merge into one sheet, normalized.
Export as CSV or Excel. Same-layout files merge automatically next time.

No. Everything runs in your browser using JavaScript — your files are never sent to a server.

Yes. Add as many source files as you want; each distinct file layout is mapped once and remembered.