So potentially 95% of passengers are packing heat? I'm surprised there aren't more fire fights with shop staff at the overpriced Pepsis on sale.
Even if your buyer did produce an assault rifle from their panties, there are still enough cameras and security around to put a halt to them after they've emptied a clip into your face. It'll be too late for you, but not for your coin.
Armed robberies usually end with the victim's compliance, no bloodshed. A pistol covered from CCTV but revealed to the law-abiding/defenseless victim, or even the 95% believable threat of having a pistol, will do.