[drc]

Mantle did signings with UDA (Upper Deck Authenticated) so UDA Mantles are reliable. Witnessed in person. Though UDA's will probably bring a premium in price.

Duly note that Travosty is harsher than most anyone on PSA and JSA. Those two companies offer good opinions on autographs, but can make mistakes from time to time. PSA and JSA's opinion is definitely worth something.

A key is to buy from reputable sellers, especially reputable in autographs. Gather a list of good a autograph dealers and check on what they have.

I happen to know of the ebay seller in your Mantle link. I think he specializes in game used not autographs, and I've never bought from him, but think he's a reputable enough seller.

Mill Creek is a reputable and well known dealer.