It is a minefield, that's for sure. Here are two Lennox Lewis sigs that are both 100% genuine (I got the card; a friend got the ticket):
With that degree of variation I can understand how genuine stuff could be mistaken for fake and vice versa. I am probably going to go with an insert card to get a genuine Tyson autograph since he seems to sign for pay whenever a card co asks.
I'm not sure he's going to be that prolific a signer at the IBHOF. I was talking with a friend who has been going for years and he says that the HOF is getting more and more stringent and security conscious about the big name fighters and that it has become harder and harder to get to them for signatures, even at the 'vip' events. I asked him to take a few cards for me (one card for each inductee) just in case and he didn't even want to try, and we've been helping each other out with autographs for years at boxing events.