I get this crap from some sellers even with verifiable pre-1899 antiques. In this case, my FFL gives me a copy of his FFL license, and I forward it to the obstinate seller who is too dumb to understand the law. I have the gun shipped to my FFL. When it arrives, I go there and open it to show him it doesn't require a transfer. He gives me the gun, and I give him $10 or $15 as a tip for accepting delivery. He does not enter it in his book because it isn't required.
There have been some instances where the requirement to do an unnecessary transfer intrastate has been a deal breaker for me. It isn't required by law for long guns in my state, so hard-headed sellers who insist upon it can just keep their gun unless it is a screaming deal.