@Anonymous if a guest is at all paying attention, they likely can get ABB to override any cancellation policy with either a complaint or Extenuating Circumstances. They should certainly cancel with ABB first & then from there see how much more, if any, you will refund. I'd rather have someone gone rather than resenting the stay: taking too much amenities, leaving on lights, blasting AC, bad review, etc. If a guest realizes that they'd rather be elsewhere, I'll likely agree with them.
Because the only thing worse than not getting paid for an empty space is not getting paid for a space that a guest occupied (but that's my business proposition - I don't have to be 100% occupied).