It's your property and you have complete control over it, unless he was an equity partner or gave /loaned you money for the property. 

There is no way to control this or know in advance if it will happen.

Where can I call to check if a property is under rent control?

The risk involved in possessing an abandoned property is controlled and mitigated by diligence in ascertaining whether the property has in fact been abandoned, why it was abandoned, and whether heirs are likely to make a claim. 

I saw this article in today's Washington Post and I thought I'd share.

http://www.washingtonpost.com/wp-dyn/content/article/2008/03/08/AR2008030802735.html

The problem therein occurs with cashing out of equity and reinvesting this "false income" (passive, and non-taxable with the right CPA) is controlled by inexperienced investors.

The general partner controls the day to day operation of the partnership and is liable for all business debt where as a limited partner is not responsible for business debts and/or claims.Liability of a Limited Partnership.

Lease options are a great way to take control of a property without owning it.

You can't market a property properly until you control it or if you already have an interested buyer.

As far as the plan to acquire more properties, the seller and I have talked about the other properties that he controls (11 properties, 37 units) as he is looking to retire after 35 years of being a landlord.