The value of a Pokémon card depends on a number of factors, including edition, condition and shadow, as well as which Pokémon is on the card. Agencies such as the Professional Sports Authenticator can also help in identifying the worth of a card.
A first-edition card, denoted by a small symbol in the middle left of the card, can be worth 10 times as much as one that is another edition. The condition of the card also plays a large role, and having cards PSA graded can help determine condition. For example, a mint-condition (PSA 10) card can be worth up to 50 times as much as a poor (PSA 1) card.
Lastly, the level of shadow, meaning level of detail, can affect a card's worth. A shadowless card is distinguishable by a production date of 1999, as well as smaller text and darker pictures.
Many common cards are worth mere change or maybe a few dollars, but a first-edition PSA 10 Charizard, a rare card in itself, can be worth about $3,500.