Cross-listing solves the "which platform will this sell on" problem for buyers — it doesn't sell to whichever platform, it sells to whichever platform a buyer shows up on first. That's good for sales volume and slightly annoying for bookkeeping, because the cost of the item was fixed at purchase, but the fee taken out of the sale depends on which of the two listings actually converted.
The bookkeeping problem cross-listing creates
Track profit per platform in two separate spreadsheets and cross-listing breaks the habit immediately — an item bought once and listed twice doesn't have a "Depop cost" and a separate "Vinted cost," it has one cost and two possible sale outcomes. Recording it in only one platform's tracker means the other platform's sales go unlogged; recording it in both risks double-counting revenue on an item that only sold once.
What actually needs recording
Three things, once, regardless of which platform sells the item: what it cost, what it sold for, and which platform's fee actually applied. The profit tracker logs exactly that per listing at the moment it's marked sold — cost basis entered once at listing time, sale price and platform fee pulled in once the sale is confirmed, whichever platform that turns out to be.
Why this matters more once you cross-list
A seller working one platform always knows where a sale came from. A seller cross-listing to Depop and Vinted has two live listings pointing at one piece of inventory, and needs the sold-status update on whichever platform actually converted to be the thing that closes out the profit calculation — not a manual note to self to update a spreadsheet later. That sold-status sync is also what prevents the double-sale problem described in avoiding double sales when cross-listing; the same underlying fix — treating both listings as one inventory record — is what keeps the profit numbers honest too.
Pricing with both fee structures in mind up front
Because the fee actually charged depends on which platform sells the item, the price itself needs to hold up under either fee structure, not just the cheaper one. That math — and where Depop's and Vinted's cuts actually diverge — is broken down in Depop vs. Vinted fees for cross-listers.
Conclusion
Cross-listing multiplies where an item can sell, not how many times it can be sold or how much it cost. Keeping one profit number per item — updated once, whenever the sale actually lands — is what keeps cross-listed bookkeeping from turning into two half-accurate spreadsheets.