What's a collectible card worth
Practical guide
The price of a collectible card (Pokémon, Magic, Yu-Gi-Oh!, One Piece and other TCGs) isn't a fixed number: it depends on several factors combined, some tied to the card itself, others to the market at a given moment.
What affects the value
- Rarity and print run — how many copies of that card, in that specific printing/edition, exist in circulation.
- Edition and variant — first edition, foil/holo version, an event promo: the same artwork can have very different values depending on the printing.
- Current demand — a character becoming popular again (a new animated series, a new set referencing it) or a card being relevant in competitive play can push demand up regardless of its original rarity.
- Physical condition — all else being equal, it's the factor the buyer controls least and the one most disputes center on: an identical card can be worth noticeably more or less depending on how well it's been kept.
Why condition is a multiplier, not a footnote
Two copies of the same card, same printing, can have a wide price gap depending on condition. That's why the market developed standardized grading scales (PSA-style, 1 to 10) that describe condition with a number instead of subjective adjectives like "good condition" — two people can mean different things by the same phrase, a number cuts down that ambiguity.
Where to find a reference price
Collector marketplaces (e.g. CardMarket in Europe) show both the prices asked by active sellers and, where available, the history of sales actually completed: the latter is a more reliable indicator than the former, which can simply reflect what a seller hopes to get, not what the card is actually worth on the market right now.
If you want an idea of your card's condition before deciding what to do with it, you can try a scan with TCG Grading Portal: upload a front and back photo and get a PSA-style grade estimate with a detailed report.