I was at an auction about 10 years ago where some guns were found and sold on the spot.
The auctioneer or auction house may have had a license OR if they are firearms made before 1893 I think is the date they can be sold in public sale without seller having a firearms license. That is why on Pawn Stars all they buy and sell are old guns. On Cajun Pawn Stars it's obvious the owner does have the federal license. I know on Pawn Stars they have said many times they could not and would not purchase new weapons due to not having a federal firearm license. That's one of the reasons they have the guns checked by experts. A mistake of even a year can be a huge legal problem.