I don't disagree with any of what you said. however one still can not provide proof that one ask for and were shown a permit unless copies or info were recordedContacting someone via PM does NOTHING to prove in any way, shape, or form that the buyer isn’t a convicted felon, or otherwise prohibited to own or possess a firearm.
A look at the buyer’s WCL would go a long way to showing that the seller made a “reasonable” effort. That term is used a lot in the law.
A prosecutor could make an argument that the seller failed to make even a minimum effort to confirm that the buyer wasn’t prohibited from owning a firearm. An argument that would take an attorney and money to fight. The prosecutor takes their argument to the Grand Jury, which is made up of your “peers”. As someone who has testified to Grand Juries more times than I can count, I can see the possibility of getting them to buy that argument. Now you’re charged and have an expensive legal battle on your hands.
Do you have any idea how long it would take an LE agency to go through the steps that you just described? No, you don’t, because you have no frame of reference for it. In the meantime, there’s a possibly that you are being detained. That’s a lot of fun.
FWIW, I don’t do bills of sale, and I can’t remember the last time I required someone to produced their toter’s permit, but I understand why some folks require it.