Also, I’m not sure if there is a law regarding this, but the last time I sold a gun on the “fire” I got a call from the receiving FFL tearing me a new one and threatening to send it back since I hadn’t included a copy of my drivers license.
Not being a dealer and having shipped many guns to FFLs, I've never shipped to one that didn't require this. When I receive a gun my FFL requires a drivers license as well and he will not accept the transfer without one. It should be made clear before the gun is shipped though.