DO make the distinction between enthusiasts who set up a table at a show, (and may do it on a regular basis) to sell or trade items from their collections (which is entirely legal) with the guy who sells his "private collection" of 15 Lorcin .380s, and the next show has another private collection of 15 different Lorcin .380s...
And I would bet a fair amount of money that 95% of the former will do a bill of sale, will require ID (to prove you live in state), and balk at any request for "no paperwork." The latter? If there was a shady group at a gun show, they would be the ones. And it's easily enough proved that what they're doing is illegal anyway.