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Merge Shopify and Mercari Sales Data for Handoff to Your Accountant

Handing raw multi-platform exports to an accountant usually means paying them to do the cleanup you could do yourself in a few minutes.

Why Shopify and Mercari exports don't line up

Shopify: a Created At timestamp that includes a timezone offset; a single Total column that already nets out discounts, with tax broken out separately; an order Name like #1001 rather than a numeric ID. Also, exports one row per line item by default, so an order with 3 products becomes 3 rows unless you export the summary report instead.
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 handoff to your accountant, 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 Shopify 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.