Most of their customers would stop using it then. They use AirBnB instead of some swank hotel in large part for the cost. Even if the deposit was just a temporary hold of their funds or credit, that would be a huge turnoff to a large chunk of their customer base.

500 to 1000 is not bad of a seed funding for a thief. I think better security measure would be to provide some sort of valid state or federal or national identifications. Any decent hotel requires this so why not AirBnB?

I would pay to be verified by AirBnB, by uploading a picture ID and having a human verify this. A service I use provids added verification by mailing you a code that you enter on the site to prove your address. Things like this could help a lot to assisting with identity scams.