Is there a reason that people throw manners out the window when dealing with cashiers?

I’m a cashier at wawa and I just wonder what makes people think that barking cigarette orders in place of returning my greeting. Talking on the phone when I try to ring them up. Putting money all over the counter instead of my open palm. snapping at me when the price isn’t what they thought, is a-ok. I could go on and on (really I could). Im not so much mad and this is a real question not a vent. Do you think people feel entitled to be less civil with cashiers because we’re getting paid to deal with them or as a collective are people are too busy to be polite?