Background- I manage a retail store.
On my day off a customer came in requesting a refund, which they were entitled to. Newish guy working that day called me to confirm, I authorised and he processed it.
Unfortunately he processed it at full price when the item had been originally bought at a substantial discount.
We caught the mistake the following day, contacted the customer and made arrangements for them to pay back the difference. They were understanding, a little embarrassed that they hadn't realised initially and paid us back straight away.
All in all it went very well, at least, as much as it can after what could have been a pretty big stuff up.
My question is, what would you do in the same situation?