OK but like any document, I assume that can be forged.
It's clear that you don't know guns, and are asking a lot of questions, as well as making assumptions that aren't true.
So, why do you feel it necessary to caution other folks, and offer opinions, on a subject with which you're not familiar?
OP - Selling to a prohibited person is/can be a crime. That's the risk.
But selling on Gunbroker works, because you ship to an FFL. That FFL will ensure that the buyer meets all requirements for their locality. No prohibited person will get through the FFL.
Selling to a local person with a CC permit ensures that your buyer is not a prohibited person.
Placing the gun on consignment at a local shop, or selling outright to a local shop, also prevents the sale to a prohibited person.
All the options suggested are good, and keep you clear of any potential issues. Pick the one with which you're comfortable.
Edit: wish you were closer, I would love a 686...