We have accepted one alteration request in the past because of a weather issue/airport closure and the guest not being able to get here. She altered her date by a few days and then cancelled (within our flexible -at the time- cancellation period) claiming it was too much stress to arrange flights back etc. We felt sorry for her since she was unable to visit, but we were out that booking since it was last minute.
We now have a moderate cancellation policy and do not accept last minute alterations that leave us with unbooked days.
Recently another alteration, which we declined this time, was the day of the booking and the proposed dates in the future were a schedule conflict which I just had not blocked out yet. The reason was illness but this was last minute and with the schedule conflict - we declined the alternation and suggested they go through Airbnb's extenuating circumstances process.
They cancelled (since we declined the alteration) and then put in a request for money back stating that they felt one day of compensation was fair enough for us. I guess they had not read the cancellation policy or felt it was easier to get a partial refund from us rather than Airbnb. The guest was appealing to us and not going through the extenuating circumstances area with Airbnb to get a partial refund. After asking Airbnb about this case …in the end, we went with enforcing our cancellation policy and declined the request for money back.