If you're that worried about it, contact the gun show people. Maybe they can give you some contact information for the seller.
As far as keeping records, I prefer to keep more records than I have to. Showing them to anyone is optional.
CONTACT YOUR SENATORS, REPRESENTATIVES, AND GOVERNORS, AND TELL THEM YOU OPPOSE FURTHER GUN CONTROL!
They're politicians. If you identify yourself as a voter, they WILL
listen. It's IMPORTANT, and the NRA makes it EASY!