I am in the process of buying a rifle currently from a site member in Scotland. My RFD is in Wales but I live in England. Both seller and I were told that I was to post my FAC to the seller (who is a complete stranger to me), so I have contacted Gwent Police Firearms Department to clarify.
They have said that sending my FAC to the seller is unnecessary, and also poses an unnecessary security risk as it would provide a complete stranger with my full name, address, DOB, photograph, signature, FAC number and a list of all the firearms that I have access to! It is also probably a fair assumption that someone with firearms may also have shotguns. This could then potentially be passed on to a third party either as information or as the original certificate. When I spoke to the FEO afterwards, he also suggested that such a move could be deemed in breach of my FAC conditions should anything go wrong! In addition, you are supposed to keep your FAC secure, and report its loss immediately, but sending it to a complete stranger at the other end of the country is fine!
His direction was for the seller to transfer the rifle to his RFD and as method of transfer write 'sold via RFD transfer'. The rifle is then sent to my RFD via their usual route, and I collect it and put 'Purchased via RFD transfer' on my license.
It appears that sanity has won!