The question isn't "what's this worth" — it's "what's the most I can pay and still hit my target profit after fees, prep, and shipping." Working backward from an expected selling price to a maximum purchase price turns a gut-feel offer into a number you can defend, and it's the same formula ListNestly's built-in Deal & Profit Calculator uses.
Maximum purchase price
expectedSellingPrice − sellingFees − shippingCost − prepCost − targetProfit − riskAllowance = maxPurchasePrice
Example (illustrative): Say you expect to sell a tested space heater for $60, with an estimated $6 in marketplace fees, $0 shipping (local pickup), $5 in cleaning supplies and time, a $15 target profit, and a $5 risk allowance for an unexpected fault. Maximum purchase price = $60 − $6 − $0 − $5 − $15 − $5 = $29. This is an illustrative example — plug in your own numbers.
Where the expected selling price comes from
This formula is only as reliable as the selling-price estimate feeding it. Base it on genuine comparable listings for the same item in similar condition on the platform you'll actually sell on — not a guess and not the item's original retail price. If you're unsure, price conservatively; overestimating the selling price is what turns a "good deal" into a loss once it's actually time to sell.
Why a risk allowance belongs in the formula
Used items carry uncertainty a formula built purely on the visible condition doesn't capture — a fault that only shows up once you actually power something on, a part that turns out to be missing, or a selling price estimate that turns out optimistic. A risk allowance is a deliberate buffer subtracted before you ever make an offer, not a number you hope you won't need.
Where this lives in ListNestly
The Deal & Profit Calculator (in Tools, after signing in) runs this exact formula — purchase price, repair/cleaning/transportation costs, expected selling price, delivery revenue, and selling fees in, profit, margin, ROI, and a break-even price out — so you don't have to run the math by hand every time you're evaluating a purchase.