Have him mail you the F4 sign your name, send it back to him. I understand charging , as paperwork (sucks) and is time consuming. However IF it's filled out like other FFL's do a signature here , check off there you're GTG. I have to look at a F4 to verify what you as the buyer need to sign , etc.
IF it's a trust The TRUST NAME,, NOT Your Name goes in (F4) 2a. It's the one mistake often made.
AND people forget (ok some ffls do) to include TRUST after the name of trust. I had one kicked back due to FFL ignorance of paperwork.