Here is a quote from a thread on the subject. This has been debated before.
Link to thread:
Gunbroker FFL QuestionRe: Gunbroker FFL Question - 07/08/17 by 45_100
As a FFL dealer (actually a manufacturer) I registered on gunbroker.com to ship and receive firearms. I don't ship many firearms because an unlicensed person may ship directly to a dealer. I accept firearms from unlicensed persons and appreciate a copy of their drivers license but don't require it. I do need their address for my log book. Copies of FFL goes into a file separate from the 4473.
In my area I have the best luck with USPS but we are a small town and the people at the PO know what I am shipping. Don't make any reference to firearms on the package or in the names of the shipper or receiver. The less information you reveal to the shipper the better
I also asked my FFL dealer. He said that in the past (I believe he meant before he had his FFL by in the past) the way he dealt with it was to provide a copy with all information blocked out except his name, photo and address. I had this issue come up and went through with the deal the first time I encountered it. I only went through with the deal because I didn't want to disappoint the buyer who was a good guy. His FFL dealer wanted ALL the information. If you ever had your identity stolen using your DL (mine was stolen from a locker years ago), you'd understand the hesitation. The state comptroller of Texas seized my bank account, sucked it dry and left it with a very large negative balance. Someone had started a business in my name, never paid their sales and uses taxes, rented an apartment, skipped out on rent, deposit and utilities.
