The value of a collectible sports card is most easily calculated by looking at completed eBay auctions for identical or similar cards. However, not every card has a comparable sale on eBay, so printed price guides, such as Beckett Media and F+W Media, are the next tools to consult.
Looking for completed card sales on eBay involves entering a card in the search box and clicking on the "Completed Listings" box in the filters bar on the left of the results. Any sale that happened for the last 90 days is displayed, whether it was completed or not.
Sports Lizard and Terapeak are online subscription services that provide sales information and projections for future prices. Both services offer sales histories for at least a year on cards or sets. This allows collectors to track certain sales trends and predict how the value of their collections may change over time.
There are several monthly price guides and online supplements for graded cards and sets. Most of the pricing information is taken from shows, auctions, stores and online dealer sales. These are ballpark figures, though, since they cannot assess the condition or the grade of a specific card. Vintage card collectors are also fairly accurate sources for pricing.