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Merge Amazon Seller Central and BigCommerce Sales Data for Tax Prep

At tax time you need total revenue by channel without hand-fixing each export's columns first.

Why Amazon Seller Central and BigCommerce 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.
BigCommerce: an Order Date column that includes a full timestamp; Subtotal and Grand Total both included, which are easy to mix up when mapping; a numeric Order ID. Also, many optional columns are exported blank depending on store configuration, which can throw off auto-mapping by header position.

For tax prep, 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 BigCommerce 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.