Here's the question I posed to the "reputable" seller.... Needless to say I didn't get a "reputable" reply.

"What kind of documentation can you offer to verify that this card legitimately belonged to Mickey Mantle (the Yankee Hall of Famer) and not some shmuck by the same name ... or by someone with access to an embossing machine and a stack of Taj Mahal blank slot cards that are prevalent in the hobby?