If everyone played nice and actually put a copy of their Valid state D/L or some other form of official State or Federal ID w/ Picture in with the firearm that you can read,,that would be a good step.
Trying to get the needed information after the delivery is near impossible, and there you sit as the FFL with a firearm in your lap w/no ID to show where it came from. The mailing lable doesn't cut it in an ATF compliance check.
You can't just send it back to the mailing address either as that requires an FFL at that end if out of state. ,,,and who's going to pay for that shipping. Mean time the customer of yours is standing there wanting 'his' gun but you can't transfer it to him.
You could enter the gun in your book as a 'repair' and then send it back to the same address,,that's legal to do IF it were true. But it isn't. Making false entrys in your bound book is a felony. Wanna take a chance? I'm sure no one ever though of that trick before...
If it does come with proper ID/DL, great,, log it in. Call your customer. He comes down, takes one look at the gun and says, 'Nah, I don't want it'.
Now what does the FFL do?
I can't send it back to the person who sent it as they are not an FFL,,same problem as above even if your customer has agreed to pay for the return trip/3 day insp/refusal.
So are you as the FFL supposed to find an FFL in the sellers state and secure a lic copy from them to send the gun to so it can be sent there and then transfered to the orig seller,,was that part of the deal,,is that on my free time?
That's why most FFL's simply say, accepted from another FFL only.