Welcome to the site!
If you're talking about buying a gun directly from an individual, then there is nothing you are "required to do or tolerate". The seller sets the conditions (including the price), and the buyer either follows them, or doesn't get to buy that gun. If there is something that you don't like about the terms or the price, you can tactfully ask them about it, and based on the answer, maybe negotiate a bit, but if you want the gun badly enough, you follow the set terms and pay the price, or go and buy somewhere else.
At least that's the way it works when I sell a gun.
Is there something specific you were wanting to know about?
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)