Yes, @Louise337 , as you say, they can ask for anything. I have twice had alteration requests made for dates that had been already blocked by the system for prep. I reported it each time and was told it is a known glitch and the developers are working hard on fixing it. Must be a tough one...
It's annoying, because it makes the host the bad guy, when it would be simpler if the system just handled it - our blocked days, our min/max stays.
Do stick to your rules. I didn't the first time it happened, and I regretted it. The guest wasn't at all bad, but trying to do a same-day turnaround on a very inconvenient day for that was ridiculously stressful and I had brought it on myself, which left no one to blame. 🙂