If you’re a guy: Take a hint and be aware that the woman you’re hitting on is in a situation where she is obligated to be nice to you. Smiles and friendly behavior are 99% of the time just her trying to deliver good customer service.
If you’re a girl: Pray he takes the hint, pray he leaves you alone, pray he’s not gonna be one of the guys that gets angry at rejection, pray he’s not gonna wait outside for your shift to end. Probably call security to walk you out again.