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Merge Poshmark and Mercari Sales Data for Monthly Sales Reporting

A monthly sales report across channels needs one date format and one revenue column, not a per-platform patchwork.

Why Poshmark and Mercari exports don't line up

Poshmark: a sale date in the seller's local time; listing price and the Poshmark commission shown separately; an order number tied to a single sold item, since bundles are the main exception. Also, the export is aimed at individual resellers, so it has far fewer columns than the bigger platforms and no shipping/tax breakdown.
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 monthly sales reporting, 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 Poshmark 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.