I like Colt Diamondback revolvers (and Colts in general). A number of years ago, a person on a forum indicated he would be interested in selling some. He said that he had quite a few. I commented and wondered how he amassed such a collection just for conversation and interest sake. He reacted very negatively and I never heard from him again. I found this odd.
Do you think this person would want to provide a receipt?
With regard to the erasure of NIC check data... I have seen no proof one way or the other in terms of not accumulating this information into a larger and organized database/registry. I would think folks from BATFE would be very willing to state that this information is not saved (regardless of the law). But you don't see such a comment. Stating what the law is does not convince anyone who might be suspicious of government intrusiveness. It is a circular kind of discussion with no absolute answer.
The receipt discussion strays from the focus of this thread and has been discussed many times on the gun forums. I personally prefer a receipt on face to face sales, but it is situational.