I don't really have a problem with it. Guy is the owner of the gun, after all, he can set what terms he wants for its sale.

It may cover your ass. I don't really care. I don't like having guns "traceable" to me, on principle; I don't like our system of not-really-but-sorta gun registration. So I get them privately when I can. I won't ask for or participate in a transaction where someone wants my liscense.

Still, if the ATF ever came to me about a gun used in a crime, the story will be the simple truth: "Sorry dudes, sold that one privately some time ago."