Price guides give a high and low book value (BV) for any particular card. We like the online price guide offered by Beckett. You can subscribe to their site for a low monthly fee and have access to all of their current baseball card listings. Beckett makes it very easy to search their site for the cards you want to look up. Beckett also puts out a monthly magazine with the same price information. The rarety of a card strongly determines it's value. If you have a card that is a short print then it is going to be worth more than a common card. Short prints are only printed in a limited quantity- meaning that there are only so many made. Generally, the fewer the cards the higher the price. The quality of a card also strongly determines it's value. The quality is determined by it's grade. I mention more about grading a little later on. Simply put, if a card is in mint condition then it's value will be the highest. If your card is off centered, has rounded edges, fingerprints, holes, or paper clip marks then your card is worthless except for what it is worth to you as a part of your hobby or investment and as with any type of investment, we recommend you do your homework before investing in sports cards.