The camera is on when the property is supposed to be empty, that is, when the alarm is armed and the guest is not there. The camera is for monitoring the property with a guarantee that the guests are not monitored. This is similar to how a hotel works. I expect the hotel management to be able to go in to my hotel room when I'm not there (to repair something, clean etc.) but I also expect complete privacy when I'm in there.

I have cameras in my house that are used together with motion detectors as part of my home alarm system. If the alarm goes off I can see whether the alarm was triggered by my christmas tree falling over or by a burglar. They aren't used when the alarm isn't on. If I were to rent my house out on airbnb I'd probably cover or disconnect the cameras, becauuse I couldn't make a guest trust that they are only part of the alarm system. That's why a product that guaranteed it would be good.

I think the point in this example is that you can compare pre-check-in and post-check-out photos and demonstrably show damage or (visible) theft occurred during a specific reservation without impact the privacy of the guests.