Some of these sales have been confirmed by the sellers over on NA. From what people are saying, it appears to be one guy, and I don't believe he's part of NA or any other forum for that matter.
Having sold a sealed title in the five-figure range (and numerous others in the four-figure range), I can assure you these sales do indeed exist. Would I ever spend that type of money on a sealed NES game? Fuck No!!!! But you're damn right I'll sell one for stupid money. I'd rather have a brand new bathroom than a game in an acrylic case, but to each their own I suppose.