As others say, the RFD is only acting as a 'post box' as they are allowed to receive a firearm by post whereas everyone else isn't.
Accordingly, neither RFD (sending or receiving) is selling you anything beyond the service involved sending/receiving, you are selling to him and the SGC records should reflect this, i.e. off yours and onto his.
When I have made remote purchases, I have sent my SGC/FAC to the seller who completes the necessary information and then sends my SGC/FAC back to me. They then take the gun to their local RFD who sends it to mine. I attend my local RFD once the gun is received who checks that I am the SGC/FAC holder and that the gun is entered on the SGC/FAC. They then let me take the gun (it's mine, afterall) and I pay them whatever fee they charge for receiving.
I can't see a strict need for the sending RFD to see a SGC/FAC, their concern should be about verifying the identity and address of the receiving RFD (I once had an RFD (who will remain nameless) post the rifle to an incorrect address, needless to say, that was a stressful few days).