If fish ru B t If fish rub themselves on the side or bottom of tank its usually means they have parasites on their body. When ive bought my koi new fish often show this behaviour and i have to treat with anti parasite to clear it.
I think you went beyond your commitment. I would have offered some discount as is normal with extra scutes. The main thing is your customer is happy and you have shown to honesty to resolve the issue. Good luck to you.