Tell ya like I just told my 6 year old grand daughter that doesn’t want to go to bed “ there is a fence post in the yard I don’t believe you’ve argued with yet”.
Op, if in doubt make em whip it out. ID or weapons permit but you have no obligation to “investigate” or run a bgc on a buyer.
Once it leaves your possession and it was sold pfft let em knock. You didn’t pull trigger or brandish it. Not your problem. And if it’s someone here in ODT if sale was done and documented IN PRIVATE MESSAGE. you’re good.