The property owners dont have time and dont want anything to do with your site. In fact, they are probably oblivious to your site's existence. How are you going to prevent harming properties' reputation without any involvement from the properties? Because, one way or another, their reputation is at risk through your site.

You should look into how tripadvisor deals with hotels. I believe there's been lawsuits, but the tripadvisor is powerful.

By the time the site gets big enough to make a dent in the properties' reputations, that will also be around the time property owners start hearing about it.