Nasty part of computers, something those things do not work. I remember a day at Krabi Airport, total black out, all foreigners stamped in by candle light. No problem, all in the database the next day. Shopping at
****
, no problem she writes it down and use a hand calculator for the change. Never ever I have to go back the next day to check if they really did their job. But if you do not trust them, your only option is go back and hope the computers work to satisfy your feelings.