It would be useful to be able to either block or show a warning on the POS if the user tries to return an item and this would require them to give more cash than is in the till. For instance, the system could use the "short" amount to know how much cash should be in the till, and if a return is attempted that would be greater than the short amount, the POS could display a warning that there is not enough cash in the till to complete the return if trying to return in cash.