1. Start with condition
Scratches, whitening, dents, bends, and surface damage can lower value. A rare card in poor condition may sell for much less than a clean copy.
2. Match the exact printing
Cards can have several versions. Compare the same set, number, language, foil treatment, promo stamp, and edition before trusting a price.
3. Look at sold prices
Asking prices can be wishful thinking. Sold prices show what buyers actually paid.
4. Watch demand
A card used in popular decks can rise quickly. A card that gets reprinted, banned, or replaced can fall just as quickly.