there seem to be issues on both sides of the deal... The seller clearly has a different opinion on the grade of this machine than the buyer and some others do. At the same time, it would be far fetched to say he misrepresented the product. Nonetheless, there is disagreement about the quality. On the other hand, it is standard business practice that all sales are final on the purchase of antiques/collectibles. Best case scenario, buyer is required to pay for return shipping, unless the product was damaged in transit. So on one hand, you have a product that's not as nice as it seemed and on the other you have buyers remorse and an unwillingness to pay return shipping costs.

The fact that the buyer is "threatening lawsuit" is a joke... First, that's no way to handle your business while legitimate options are still on the table. Perhaps ask for a partial refund because the product was not "as described"? Second, it's unreasonable to think anyone would be willing to pay $3000+ in lawyers and travel fees to recoup $2000+ (and would still have to find some way to return the merchandise most likely!). Third, anyone who continues to threaten like this hasn't really contacted a lawyer because a lawyer would immediately advise him to shut up.

If you're feeling guilty as the seller perhaps offer a partial refund ($500 or whatever your margins can afford) and ask him to sign a paper stating that the sale is final and that returns are not accepted.