Just out of curiousity, I set a match where the only items available were Smash Balls and Fake Smash Balls. After playing several matches, I could not find anything obvious between the two in the heat of battle. I do have a few assumptions. From playing it seemed that the fake smash balls were the ones that dropped straight to the ground like an item, instead of floating around like real smash balls.
But the problem is that even fake smash balls can also float around like real ones, yet I could not recall finding a real smash ball that dropped to the ground. Either I didn't notice, or it dropped off the stage.
That said, I am honestly curious if there is any discernible difference between real and fake smash balls.