You can bet they wouldn't be coming to his house to pay him more if they found out they cherry picked him! Bust a deal, face the wheel!
The lesson to be learned here is to ALWAYS educate yourself BEFORE buying or selling, NOT AFTERWARDS. But, there's no excuse on the dealer's part. If the coin was slabbed by a reputable grading service, then it was real, and WHY IN THE HECK would they have taken such a coin out of the slab in the first place, anyway?