I was once a cashier but never had a single customer complaining against me.. Idk, but i dont remember a single time i frowned infront of a customer, nor mumble a bad word. Though most of the time customers can really make me stomp my feet for using their mobiles while i am checking them out, and in the middle of their phone calls they would be asking me something which i will barely understand because at that time i am focusing on cashing out their items rather than listening to her conversation. if i am like "i'm sorry sir?" He will be yelling at me like he was the one who brought me to here on earth. What he will get from me? A sweet smile and another , "i'm sorry Sir, you need what?"