In The Ten Ring said:
Why would I do a bill of sale?
Simple. If the gun is ever linked to a crime I want something in writing I can fall back on. Although I would much prefer the pre-1968 laws, I do my part to be sure the buyer isn't a criminal of some sort. Anyone not willing to show ID, allow ID info to be copied down, and sign a bill of sale, is suspect in their intentions.
This post is illustrative of the dilemma faced by many gun owners. No responsible gun owner wants to sell a firearm to a prohibited person, but many responsible gun owners want to buy their guns (at least some of them) without leaving a paper trail for the government to follow if things deteriorate to the point of confiscation. They also don't want to get dinged if a firearm they sold is subsequently used in a crime.
The arguments for and against bills of sale and copying identification data have been discussed on this and other forums countless times. I doubt there will ever be a consensus. The closest I've seen suggested that somewhat satisfies both sides is to ask a prospective buyer to show proof of eligibility in the form of a carry permit or FOID, but not to copy down the information. That way, the seller has made a proactive attempt to ascertain that the buyer is legal -- but he can't prove it in the event of a problem.
It's not an issue for me because I live in one of those states that doesn't allow face-to-face sales without a government permission slip. (Which, of course, only ensures that such transactions are carried out by the very people the law is intended to prevent from carrying out such transactions.) I wish I lived in a state where I could buy "off paper." That said, perhaps because I have become accustomed to paper trails, if I were selling I think I would do so through an FFL even if not required, because that gives me the comfort of knowing I have proof that I no longer own that firearm.
A private person cannot do a background check, even a C&R holder cannot. If you want to "see if the gun is clean" you will have to go through an FFL and pay for it.
Again, each state is different. In my state, private sellers MUST do a background check. It's done through the State Police, not directly through NICS, but it is mandatory for private sales. But, it's on the buyer, not the gun. Even a background check through an FFL doesn't assure that the gun is "clean."
We simply cannot generalize on any of this stuff. We have fifty states plus DC plus federal law. There can never be a one-size-fits-all answer to any of these questions.