Glossary

Sell-through rate is the share of listed items that sell in a period: the formula, a free calculator, a reseller example and how it differs from turnover.

What an insertion fee is, which marketplaces charge one, how free allowances change it, and why it is charged per listing — even for duplicates.

The difference between gross and net margin in reselling, traced through one worked flip: which costs each includes, and which one decides a rebuy.

Inventory shrinkage is stock you paid for but can no longer sell: lost parcels, damage, missing items. What it means and how to spot it in your records.

ROI, profit margin and markup use the same numbers but answer different questions. Formulas, one worked flip showing all three and when resellers use each.

Liquidity in resale markets: how fast items convert to cash near market price, the three signals resellers measure, and what it changes in strategy.

Days to sell measures how long an item takes to leave your stock: the formula, why median beats average, and how it differs from sell-through rate.

Inventory valuation is the zł value you put on unsold stock. Resellers can count it at cost or at a market estimate. The difference and why it matters.

What makes a sale comparable: the five match criteria resellers use, why asking prices are not comps, and how many comps a price estimate needs.

What consignment means when selling second-hand: you keep ownership until sale, the platform takes a cut, and payout terms decide if it is worth it.

Fair market value for second-hand items: a plain definition, how to estimate it from market exits rather than asking prices, and how it differs.

Average selling price for resellers: the formula, why marketplace ASP differs from yours, what it hides about bundles, and when to use median.

A final value fee is the commission charged when an item sells. Whether eBay, Allegro and Allegro Lokalnie charge it on shipping, with worked examples.

A buyer protection fee is paid by the buyer on top of the price. How it works on Vinted, OLX, eBay UK and Catawiki, what it covers and how it affects sellers.

Cost of goods sold for resellers: what to include beyond the purchase price, what to leave out, a worked example and why COGS only counts items that sold.

Landed cost in reselling: everything you pay to get an item to your shelf, from buyer fees and shipping to verification and import VAT, versus COGS.

What card grading is, how PSA, BGS and CGC differ, what PSA publishes as its grading fees and turnaround, and the break-even check for when grading pays.

Margin of safety in reselling is the gap between what you pay and the most you could pay without a loss. The formula, a zł example and how to size a buffer.

Price elasticity for resellers: why some items sell after a small price cut and others don't, how to spot price-sensitive items and test it cheaply.

SNAD means significantly not as described: what counts on Vinted, OLX and eBay, what does not, who pays return shipping and how sellers avoid it.

Unit economics in reselling means the revenue, costs and profit of a single item, from buy price to payout. The formula, a zł example and what to count.

Opportunity cost in reselling is what your money and time could earn elsewhere while an item sits unsold. A definition, a zł example and when it matters.

What deadstock means in reselling: unworn, original-condition items (DS) vs 'dead stock' that never sold, and how the word affects pricing and wording.

What NWT, NWOT, BNIB, EUC, VGUC and GUC mean in resale listings, and how each maps to the condition options Vinted actually offers in the UK and in Poland.