My personal opinion on the subject is this.
If I bought the gun "without papers" I will sell it without papers. If I had it shipped to a FFL and it has my name on it. I need at least a name and phone number to give to the atf if it's ever used in a crime. I think some of the bill of sales like the one suggested on here are ridiculous. I shouldn't have to give any regular citizen that much info on me. However I have had friends sell guns that are later used in a crime and when the cops come looking at you for it, "some guy at a gun show" just doesn't cut it. If you can't show when and to whom you sold the gun, then your left with the burden of proving you didn't commit what crime they are questioning you for. Sometimes it would be quick, sometimes it will cost you an attorney and a lot of hassle.
So that's why I always get papers if it's "papered" to me. I wouldn't ask anyone for any information I wouldn't want them having on me. I don't ask for DL # or SSN or anything like that. And before I sell I usually verbally ask your not a felon or anything right. That in my opinion is the equivalent of CYA for this type sell. IF I'm wrong I guess I'll find out when the wrong person buys one of my guns.