Madcap_Magician ... yes, while it is possible guys like this are skating on the edge, proving it is another matter.
Do you have any idea how many firearms a "serious" collector might accumulate in a 40+ year period? Selling off some portion or all of a collection might well be several 100s of firearms, some duplicates.
Over the years, I've purchased firearms at gun shows from dealers, always with a #4473 and a NICS check. Non-dealers, with as few a couple firearms to a couple dozen or more. I have to taken them at their word that it's their private arms being sold. I've also seen them at multiple shows over a number of years ... as well as a BATFE presence and have not seen the Feds giving them grief. Either they're too lazy to do their job or they're satisified.