The law is not that clear.As a dealer we have to be able to provide from where the gun came from and where it has gone.A copy of the senders id is good proof of where it came from.Every agent that inspects you has a different extirpation of the law. If you have ever been of the receiving end of an ATF gun trace you want to cover your butt.Having all the documentation you can really helps.
The seller should be glad to provide anything you ask for,unless he is hiding something.He is the one making the money,not the trans dealer.