They have to slip a hex bag close enough to the victim for them to be affected. It'd be hard to do that with the guy behind a counter. Also they're evil so they probably got jollies out of the guy dyingstrange intro to the latest episode. If they can enchant via a love spell? Why can't they just ask the man to give them the booze + money? instead they kill for man, just because.
edit: Also leave no witnesses, had they done it to the guy behind the counter the mullet dude would have been a witness to what happened. Like why would he just give them all the money in the register?