I read an article a while back, I believe it stated that about 90% of all Mantle Autographs on Ebay were not authentic. That numbers seems to line up with this article. This is why it is so hard to buy anything signed these days. I'm trying to remember who the company was, but I remember a few years back, there was a company who sold every autograph you could think of. They could get you any autograph, and it was spot on! I know eventually they were caught by the FBI (I think it was the FBI). But so much fake stuff made it's way on to the market, and it looked that good.
Currently looking for the following comic Books:
United Comics: 21,22,23,24,26
Tip Top: 173 & 184
Peanuts 1 (1953)
Peanuts: 1-4 (1963-64)