"When Faith preaches Hate, Blessed are the Doubters." - Amin Maalouf
2) the ATF is all over those shows ( I know the ATF officers in town and I see them, DEA, FBI, and all sorts of locals at those shows)
3) if some guy constantly is selling guns "from his private collection" that is going to draw serious attention. Plus ATF especially under DEM administrations-are constantly trying to catch people. I worked for a client at a gun show years ago and one guy asked me if I would take 600 dollars for a 400 dollar gun "without and papers". I told him I was a city prosecutor and that was illegal. I later found out he was a TFO trying to bust dealers
NOPE-the gunshop retains the 4473 but that is not sent to the ATF. true the ATF can use that to track down an owner but if I sell the gun there is no requirement of registering it or the second owner has no duty to register it in most states.
what is the objection to registration
1) see England, Kalifornia, NYC and NJ-all used registration to confiscate firearms
2) if the list is stolen or hacked criminals know who has guns and how many
3) criminals are exempt from it