As the reservation is now a fait de complet, you must use the resolution center to send them a rebate.
Be prepared for dissappointment.
While you are being gracious, you may be escalating a problem that may be a moot point.
The guests may still complain about the broken coffee pot in their review and you can't remove it because it is the truth!
For me that is very dissappointing.
I have stopped giving rebates for errors. If guests are unhappy about something, they are unhappy about something. Giving them money does not alleviate their dissapointment, it merely proves wrongdoing.