It's probably the best way to track the value of sports cards and sports memorabilia--or anything else for that matter. Guide books may be out of date and just an average or estimate of selling prices. eBay's "search by completed items" function enables users to look at what items actually sold for. Unfortunately, those searches will only take you back 15 days worth of results. If it happened three weeks ago, you'll have to go to a place like Terapeak Price Report to get your information. It's a valuable tool.
Now, though, eBay is expanding the information available to users starting with the Collectibles category. Search for sold items and you'll be able to see results for the past 90 days. Unsold item data will remain visible for 45 days.
While the Sports Cards and Sports Memorabilia categories aren't included in the Collectibles realm on eBay, users on the company's discussion board are already asking for them to be included when eBay expands the data to other categories in 2012.
Speaking of eBay, the $1 million opening bid for the baseball that rolled through Bill Buckner's legs in Game 6 of the 1986 World Series, helping propel the Mets to victory over the Red Sox wasn't made.
Presumably, owner Seth Swirsky will keep what's often referred to as "The Mookie Ball" for a little while longer. He got some nice publicity out of it for the ventures he's involved in. He also found out it's not worth more than ten times what he paid for it several years ago.
You can see the auction and read all about the ball here.