How to find your max buy price
The fastest way to lose money reselling is to overpay at the source. This tool fixes that by running the profit equation backwards. You tell it the sale you expect (price plus any shipping you charge the buyer), the eBay category, the Promoted Listings ad rate you plan to run, and the dollar profit you want to walk away with. It subtracts eBay's final value fee, the shipping label you pay, and the ad fee, then subtracts your target profit, and what remains is the most you can pay for the item and still hit that target.
For example, an item you expect to sell for $50 with a $5 shipping label, a 3% ad rate, and a $10 profit target leaves a max buy price of $26.30. Pay more than that at the garage sale or the liquidation lot and the deal no longer clears your target. If the number comes back negative, there is no headroom at all: the sale price simply cannot support that profit after fees, and you should pass, raise your expected price, or drop the ad rate.
Remember that eBay's final value fee is charged on the full amount the buyer pays, including the shipping you charge them, so charging shipping instead of building it into the price does not avoid the fee. The fee figures come from the same dated eBay table the breakeven calculator uses, so the two tools always agree.