Actually, I have no idea what they did.
Here's what I know:
When I discovered the ten people in my home, I called Airbnb immediately. After discussion with the Airbnb rep, we agreed that the best solution was for them to leave my house. The rep told me he would reach out to my guest, request that they leave, and call me back. He did all those things. When he called me back he told me that they understood the issue and were leaving as soon as possible.
Very shortly thereafter I got a notification that the reservation had been changed. It was worded as though I initiated the change in the reservation and the guest accepted the change. It looked exactly like a different reservation change I made a few weeks back at a guest's request who wanted to stay a few extra days. In reality, I didn't do anything, and I have no idea whether my guest did anything to "accept" the change.
Then a little while later I got the standard message from Airbnb asking me how my guest's stay was, and encouraging me to leave a review. So far, I have not done so. I do plan to leave a review, but at the last minute.
That morning, I also got a notification that the full amount of the booking was deposited into my checking account.
Then, a couple of days later, Airbnb debited my checking account in the amount of exactly 1/2 of my nightly rate.
So.... They booked for three nights. They arrived, and stayed one night. I was paid the full amount the next day. They were asked to leave. Airbnb recovered 1/2 night payment from me. It matches my Moderate cancellation policy.
My guest has not left me a review as far as I know. She did leave a very polite (but disappointed) note in my guestbook that was written after they were asked to leave. That goes a long way in my book. She took it (more or less) graciously and I don't expect a strongly negative review from her, or any review at all, actually.
As for the early booking, I was fully committed to request a 1/2 night's payment for early check-in through the resolution center, before it all fell apart. But given the circumstances and the (mostly) positive note from my guest in my guestbook, I won't be pursuing that.
The problem is that early check-in can't be arranged in advance. My check-out is noon. My check-in is at 3pm. With three rooms and two bathrooms, I barely have time to fit the window if I have guests leaving and arriving on the same day. I can't offer a service that I can't provide.
Jamie