Here's a few easy ways to tell if a game used bat you see on eBay is real. It's the same method that I use all the time

1: First, look at the model of the bat. Above the name on the barrel there should be a model (ex.: R205,P72,etc.). Then, see if there are any more game used bats of the same player that you can find and see if it's the same model.

2: Look at how the number is written on the knob of the bat. If the player signs his number in his autograph then first look at that. If he doesn't then just look for more game used bats of the player and see if the hand-writting matches. Also make sure that the number doesn't look like it was fresh. Usually you should be able to see some scraps or dirt over it.

3: Look for blue and green ink marks on the bat. Blue marks come from Major League Baseballs and green marks come from the new Batting Practice baseballs. The Rawlings baseballs that you usually find in stores like Walmart have black ink.

4: Look to see if there is any tape on the handle. Some players, like Ken Griffey Jr. for instance, always put tape on the handle and it's usually in the same pattern. I then check pictures of the player and also look for more game used bats of the player and see if they show tape on the handle and in the same pattern.