Guys, I don't have any problem whatever with people choosing or not choosing to keep a paper trail on guns they sell or buy. Do what you think is best.
I am not an attorney, so what follows is simply the understanding of someone who has spent a lot of time reading about firearms and the law.
I think that some of you are overestimating your legal burden.
For example:
I've unwittingly committed a felony
Probably not.
The requirement is that you not
knowingly transfer a firearm out of state or to a prohibited person. Similarly, you may not knowingly receive a firearm across a state line or if you are a prohibited person. There is no requirement that you go looking for evidence, though I think that a responsible person will check a driver's license or auto plate and will back away from a deal that doesn't feel right.
Further, the term "domicile" has a precise legal meaning, and you can have only one. The term "residence" does not, and is not defined in our federal firearms laws, and you can have more than one. If you have a home in Arizona that you live in all winter, and another in Jackson Hole that you live in all summer, you have two residences and can legally privately buy firearms in either location without benefit of FFL.
There is potential mischief in keeping receipts or bills of sale. If the authorities ask for information on a private transfer, and you produce a signed document for it, then they might ask, "How many more of these do you have? Five? Well, did you make on money on these? Are you aware that this might constitute dealing in firearms without an FFL?" Sadly, there is no bright line that tells how many firearms you can sell in what period of time without an FFL.
My transfers are very few. And as far as I know, Yugo M48s are not popular in our local gang culture (as though I would know). So I don't worry about enabling someone to commit a crime. I've had the good fortune of dealing with people who seemed like normal, stable, responsible people.
If asked, I can honestly say that my face to face sales have been one every year or so. And I'd rather not have a paper trail that a gung-ho enforcement agent could use to raise questions I don't want to deal with.
Similarly, if cash is exchanged for a firearm, face to face, then getting sued is not even on my worry radar.
My personal approach is that it is better for everyone if two strangers meet, cash goes one way, the gun goes the other, and two strangers part company, happy with the bargain they have made, never to meet again. If you disagree, I have no quarrel with you.