@Hazel-Ve-Rula0 If you charge a refundable key fee, it will pay you to get new keys when the guests take them and will encourage the guest to give the keys back to get their money back.
I would have it in your house rules that X dollars is the key fee, and that it will be returned via the resolution center when they return the keys. I have increased my nightly rate by a few dollars to cover costs like this -- it works out in my favor over the course of time.