Mint Condition
The value of the card depends heavily on the card's condition. Mint is the highest grading (value), and means the card is flawless to near-flawless.
Near mint
Near mint (NM) cards are worth less than mint cards, as they have minor flaws that can be seen by the human eye. A scratch or hair-line flawed corner makes a card NM.
Fair
A card in good or fair condition has significantly less value than a mint to near mint card. Good or fair cards may have rounded corners or slight creases.
Poor
Cards in poor condition are rendered worthless by major creases and flaws. The only value a poor-rated card may have is sentimental value.
Grading
Professional grading determines a specific card's value. Getting a card graded makes it easier to sell on the market.
Player
Which player is on a card also affects its value. If the player was an All-Star or Hall of Fame player, then the card's value is higher than that of an average player.