You walk down the aisle of a gun show with a firearm to sell.
A man walks toward you with a nice rifle.
You stop, talk, wheel, deal, exchange firearms and a little cash, then go on your way. And what is wrong with that?
Years ago, I could make such a deal in the first isle. Then trade of my new aquisition in the third isle.
Then do it again in the 7th isle.
When I leave I may have exchanged guns five or six times.
And how is the NICS going to stop this?
It will be illegal to transfer any weapon at all, without an FFL and the govt giving blessing. What you just described will be about five or six felonies. Or more, if the get created.