HOW WE CALCULATE PRICES
Every price on GrailGamer comes from real comps, what games actually sold for, not what sellers are asking. Here is exactly how we turn those sales into a number, and how to read the confidence labels so you know how much to trust it.
Where the data comes from
Prices are built from comps, completed (sold) listings that actually closed. We aggregate from publicly available eBay sold data and Mercari completed sales. Current "for sale" asking prices are tracked separately and never mixed into the sold numbers, because what a seller hopes to get is not what the market paid.
Game metadata (titles, publishers, cover art, release years) comes from IGDB, verified against our own catalog. Pricing data refreshes daily.
Median, not average
The headline number is the median, the middle sale price, not the average. One sealed grail or one beat-up loose cart can drag an average far from reality; the median ignores those extremes and lands on the typical sale.
We also show the range (lowest and highest recent comps) so you can see how tightly a game actually trades. A loose cart and a sealed copy of the same game will not sell for the same money, the spread tells you that at a glance.
Three condition tiers
Every game is priced across three condition tiers:
- Loose - Cart/disc only, no manual, no box. The most common condition for retro games.
- CIB (Complete in Box) - Game with original box and manual. For disc-based games, this means case + manual + disc.
- Sealed - Factory sealed, never opened. The rarest and most valuable condition.
Each tier is priced independently from its own comp pool. A game can have reliable pricing for Loose but sparse data for Sealed, and the labels reflect that honestly.
Comp count is everything
A median from 30 comps means something. A median from 2 is an anecdote. So every game carries a visible data-quality label based on how many recent comps we have:
- Reliable Pricing - 10+ comps. The median is meaningful.
- Limited Data - 4-9 comps. Enough to direction-check, not enough to bid hard against.
- Sparse Data - 1-3 comps. An anchor point only. Verify before you buy.
- No Sold Data Yet - 0 comps. We will not invent a number.
We would rather tell you "we don't have enough data" than show a confident-looking price we can't stand behind.
What we exclude
Not every eBay sale is a valid comp. We exclude:
- Lots and bundles - A lot of 10 NES games for $40 does not mean each game is worth $4.
- Reproductions and bootlegs - Repro carts are not the same product. We filter these.
- Obvious outliers - Shill bids, charity auctions, and clear pricing errors are excluded.
- Region mismatches - A Japanese Famicom cart is not an NES cart. Platform must match.
What this is, and what it isn't
GrailGamer price estimates are for informational purposes only. They are not appraisals, not guarantees of value, and not investment advice. Real prices vary with condition specifics, label variants, timing, and luck.
Use our number as a fast, honest starting point, then look at recent comps before you bid, buy, or sell.
Spot something that looks wrong? Hit the "Report an issue" link on any game page. That feedback makes the data better.
Data sources
- eBay completed/sold listings (publicly accessible, no login required)
- Mercari completed sales
- Game metadata: IGDB (igdb.com)
GrailGamer is not affiliated with or endorsed by eBay Inc., Mercari, or IGDB/Twitch Interactive. All trademarks are property of their respective owners. Platform and game names are used solely to identify products for pricing purposes (nominative fair use).