have had an 01 in the past and have an active 03 now and never had a problem with the BATF. Sounds like the folks getting questioned are doing some dealings above and beyond what would be considered collecting.
I buy a lot of C&R guns and sell a few like the others have said, but it is never for a business or profit purpose. when an agent looks in someones books and sees a lot of sales then they will only look further and nail the person in question.
as long as you don't go nuts with selling then no worries. and yes keep your records straight and keep them for 20 years per transaction. I keep both a hard and soft copy of mine (you have to have a hard copy per BATF regs and the soft copy is just for me in case my hard copy gets destroyed).
Lifetime member VFW and NRA
"Quando Omni Flunkus Moritati" (when all else fails play dead) -Red Green