I definitely see your point about the staff and how they can't know. That makes me wonder - does anyone get banned or removed from the platform? What has happened with other hosts who've been abused, scared, had things stolen etc? Sorry David that is a general question, not one I'm asking you specifically.. It's just got me thinking.
I had two guests stay here who had fled another Airbnb listing in the area. They'd stayed there for a couple of weeks, things were fine, then the host started drinking and didn't stop. He became aggressive and one of my guests beleived he'd also stolen his wallet. The police were called (for the aggression thing more so than the wallet I think) and I don't know what happened in the end but I did encourange them to please place a review AND to contact Airbnb because I felt that they would want to know that sort of information. Maybe I was wrong about the second part... maybe reviews are all we have.
Re the keys it was unclear but I think the Yvonne did say the guest 'must have' copied keys - leading me to believe that something had happened as opposed to just the general behaviour of the guest.