Condition of the Basketball Card
Probably one of the most important variables in regards to how much a card is worth is the condition of the card. If the card is in pristine condition, it will be worth full price. However, very few cards, once they are removed from the package, can be kept in perfect condition. Even the slightest bend or rounded corner can reduce its value. If you come across a valuable card, be sure to be extremely delicate with it, as if you were handling explosives, and place it into a protective sleeve.
How Many were Produced
The rarity of the card increases its value. A card that had only five or 10 copies made is going to be much more valuable than a card that was mass produced, even if it is for the same player. As a collector, you cannot control this. This is all controlled by the card producer (such as Upper Deck or Topps).
Blooper Cards
Blooper cards will be more valuable than normal cards. Blooper cards are generally cards that have something wrong with them. The name of the player might be misspelled or the wrong team logo was placed on the card or perhaps the image of the card is cut off at the top and found at the bottom of the card. These problems generally are fixed in production, so not very many of them are produced. Again, cards that are produced in fewer numbers will be more valuable than the mass-produced cards.
Rookie Card
Rookie cards generally will always be more valuable than the other cards for the same player (unless there was a limited-release card or special-edition card produced along the way). For example, a Michael Jordan rookie card will be worth much more than a Michael Jordan card the year before he retired (first or second time, take your pick). If you can get your hands on a rookie card of a top-flight player, you might be holding onto something extremely valuable.