I've used MLS, Zillow and other public databases, as well as private databases available for a fee; and although some services (not zillow, etc. but private software packages) do have interesting tools for easily pulling aggregates of properties, I can duplicate that in the MLS fairly easily.  

The reason why they are doing this for free is because they store all the landlord references in their database and allow future landlords to search for the landlord references that were submitted through their website. 

Our Screeners hand-search multiple record sources versus using an instant database that's known for inaccuracies and missing information.

Maybe have a wifi enabled smart device installed where the main water supply splits to their unit to track their water usage? 

Do you have access to RealFacts or another database with historical rents?  

@Mike Verna Can calendars be left open while "book now" is enabled?

You should be looking to add value to your visitors by building quality content consistently that enables engagement and everything else will fall into place but it is good to know some of the SEO ground rules.

Most states now have on-line free data bases to check on court actions. 

Do this a lot to add to your database.

This advertising enables you to send highly targeted traffic to your site immediately.