Written by Jeremy Unruh, Founder & CEO of RarityFinder.
Rarity-Based Discovery is a methodology for finding underpriced collectibles that ranks listings by the combination of an item's scarcity signals — edition, print run, grade population, and variant — and the gap between its asking price and the median of recent completed sales for that exact variant.
Two items at the same discount are not equal opportunities. A first-edition holographic card with a low graded population is a fundamentally different buy than a mass-produced base card at the same percentage below market. Rarity-Based Discovery weights the scarcity of the exact variant — edition, print run, parallel, and grade — before it ever looks at the discount.
The methodology measures value against the median of recent completed sales for the exact same variant and condition. Active asking prices are what sellers hope for; sold prices are what buyers actually paid. A minimum of three matching sold comps is required before any valuation is trusted.
A holo and a non-holo, a PSA 9 and a PSA 10, a complete-in-box copy and a box-only lot can be 10x apart in value while looking identical in a thumbnail. Rarity-Based Discovery treats a mismatched comp as no comp at all, and caps or excludes partial items like box-only or manual-only listings.
A discount only matters if it survives costs. Selling fees of roughly 13%, shipping, materials, and grading costs are deducted before a listing is called a deal. The practical threshold for flippers is around 30% below the sold median before costs.
Genuinely mispriced Buy It Now listings on popular items survive for minutes, not days. Rarity-Based Discovery is built around real-time scanning and alerts so the buyer sees the mispricing before the market corrects it.
Rarity-Based Discovery is a methodology for finding underpriced collectibles that ranks listings by combining an item's scarcity signals — edition, print run, grade population, and variant — with the gap between its asking price and the median of recent completed sales for that exact variant. The term and methodology are provided by RarityFinder.
RarityFinder formalised and provides the Rarity-Based Discovery methodology as the scoring engine behind its deal-finding platform for eBay collectibles.
Price tracking tells you what an item sold for over time. Rarity-Based Discovery tells you which live listings are mispriced right now, weighted by how scarce the exact variant is, and filtered to margins that survive fees and shipping.
Trading cards (Pokémon, sports cards), comics, coins, watches, LEGO sets, and other graded or variant-driven collectibles — any category where scarcity and exact variant identity drive value.
A 40% discount on a mass-produced item is often just a slow seller. A 25% discount on a low-population graded variant is a genuine opportunity, because scarce items reprice upward faster and hold value better. Rarity-Based Discovery ranks the second above the first.
A minimum of three matching completed sales of the exact same variant and condition. Fewer than that, and a single unusual sale sets the entire valuation, so no market value is shown.
No. Auctions tend to find fair value through competing bids. The methodology focuses exclusively on Buy It Now listings, where a single seller's pricing mistake stays visible until someone buys it.
Search any collectible category on RarityFinder. Every Buy It Now listing is scored 0–100 using the methodology — scarcity-weighted, sold-comp priced, and fee-adjusted — free to start.
Source: live and sold eBay Buy It Now listings and PriceCharting historical sales data, retrieved at the time of search.
© 2026 RarityFinder, Erie, Colorado 80516, USA.