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Merge Shopify and Poshmark Sales Data for Tax Prep

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

Why Shopify and Poshmark 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.
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.

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 Shopify export and map its columns once.
Drop in your Poshmark 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.