That's the question collectors have asked themselves since the first baseball cards started popping up in the late in the mid-19th century. If you've got the right cards and they are in the right condition, your collection could be worth quite a bit. The Beckett Official Price Guide to Baseball Cards is a great place to start, especially if you have some of the lesser know cards. Beckett has been a leader in assessing the value of baseball cards since the late 1980's and they are one of the most respected companies in the business.
Pros and Cons of using the Beckett Official Price Guide to Baseball Cards
Pros: Beckett has been providing card values for years. Many card dealers and shops base their pricing directly on the prices listed in their monthly magazine. The guide is great for looking up some of the more obscure sets.
Cons: The guide doesn't provide you with real-time pricing. Since the value of a card weighs heavily on a players popularity, if the popularity should slip, the value of a card could drop dramaticly. The reverse could also could also happen. Active players would be more prone to changes in their popularity than retired or deceased players.
Another way to look see how much your baseball card collection might be worth is looking up your cards on Ebay. Collectors have been selling on the site since started in the mid nineties.
Pros and Cons of using Ebay
Pros: Ebay gives you a "real-time" value of what your card could be worth. You can watch the actual exchange between the asking price of the seller and what the buyer is willing to pay.
Cons: Auction prices can rise dramaticly during the closing minutes of an auction and if your not "watching" or bidding on the item, you might not see the actual final price. Another thing to consider is that their are a lot of reprints on Ebay. A reprint is essentially a copy of the original card. You must be very careful to read the entire description to see if the card listed is an original or reprint.
I'd recommend using both the Beckett Guide as well as Ebay as tools. Use the guide to become familiar with what your collection should be worth, then look them up on Ebay to see what the real-time prices are. You could sell your cards on Ebay, but you will be subject to some fees and commissions, which definately cuts in to your bottom line. You will also need to take pictures of the cards and create accurate item descriptions. Selling to your local dealer is a lot easier. You might only receive 25% - 50% of book value, but you get paid instantly, you don't have to do any of the leg work, and if you don't think they are giving you a fair deal, you can simply walk away.