I would say that every responsible weapons dealer should go with their gut in refusing sales to people who seem a bit off. But I also recognize that such a measure can also quickly go down the path to discrimination. Perhaps a gun dealer decides that all African-Americans are shady or that someone who "looks Muslim" shouldn't be allowed to have a gun. So, I think it's a balancing act. If a guy walked into a bar completely wasted and ordered a drink the bartender could refuse service even if he provided proof that he was over 21 and had cash in hand.