@Per-Håkon0 If a guest cancels after they check in, they can still review their stay. Stop worrying about a bad review in retaliation for not refunding. You haven’t done anything wrong. Hosts should not let themselves be held hostage by this fear. If you do get a wrongful revenge review, you have the opportunity to respond and ask future guests to consider your many 5 star reviews for an truthful representation of guest experience.
When someone books with you, they have full knowledge of the terms of the cancellation policy they are agreeing to. It’s part of the contract. Why should you break that contract just to be ‘nice’ or avoid a bad review because of it?
I certainly wouldn’t encourage a guest like that to come back by offering a discount, with the high likelihood they’ll do the same thing next time.