to be an obvious fake:
Too bad, that would have been a nice item.
This sounds like a classic case of buyer's remorse. The guy paid way more than it was really worth even if authentic, realized it, and is trying to get his money back.
In any event, the buyer should have examined the items and done the needed research before the sale. If he had any doubts about the authenticity, he should not have bid.
It's not always the seller or auctioneer that is the crook.
If the item is from that time, and there is no record of it one way or the other but TE tended to give out such items, I think that finding "proof" that it's a forgery will be very, very difficult. It will be like proving the existence of a nullity, proof that something (flying horses? aliens from Neptune?) can't exist. The seller has every reason to be confident.