This is what I do. Ask for ID to show state residency and age (18 years old or older). Look for signs of a prohibited person - if the look OK/sound reasonable to me, that's all I do. If you don't like the way they look/talk, you have no obligation to sell to them.
Sign a two part bill of sale. Part 1 is theirs and will say that they purchased make/model/serial number of gun on date from me and that I have received $XXX. I sign that one and give to them as a receipt for their money.
They sign part two stating that they purchased make/model/serial number gun from me on date and that they have received described gun. I keep that one as a receipt for my gun.
That's it, for me. I don't believe in requiring a CPL (or CCW license, whatever in Texas) and I don't believe in copying or recording any of the ID information. If I wanted to do all that in a private sale, I would go to an FFL in the first place.