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Merge Mercari and Wayfair Sales Data for Quarterly Tax Estimates

Quarterly estimated tax payments depend on knowing real revenue across every channel, not just the platform that's easiest to check.

Why Mercari and Wayfair exports don't line up

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.
Wayfair: a purchase order date distinct from the ship date required by Wayfair's supplier terms; wholesale cost, freight allowance, and Wayfair's referral fee as separate columns; a Purchase Order (PO) number rather than a typical order ID. Also, built for suppliers rather than direct-to-consumer sellers, so column names lean toward logistics (PO, ship window) rather than retail checkout fields.

For quarterly tax estimates, 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 Mercari export and map its columns once.
Drop in your Wayfair 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.