Personable, but more importantly professional and a tireless worker. 

This person, as evidence by her prior eviction and her not paying you, either doesn't have any money to pay rent or is a professional tenant that moves from house to house doing this to landlords.

You never give reasons or details and if questioned you simply state that you do not release that information.Unless your state regulations state otherwise they are not entitled to know and to protect yourself legally you never say anything to rejected applicants.

What is the difficult situation, tenants not paying rent is common and the process to deal is far from difficult.Work with the guy, but for peat sake begin the process of giving the pay or quit notice asap according to your state regulations.

I did a background check and called 3 separate references from real estate professionals in the area that know Mr.

Hello fellow Real Estate Professionals,I just passed my brokers exams in Colorado, and am now searching for a Brokerage to hang my license.

You'll see local professionals who post on these forums and they can help you out. 

We, as RE professionals can limit exposure for ourselves and our clients by implementing prudent due diligence on tenants; by ensuring our tenants are properly licensed, operating within the law and keeping their operations to code the changes of the DEA / DOJ seizing assets is (in my opinion) next to zero.

Finally, always let them know of new ownership and set the stage that you are professional and are willing to work with people, but don't let them take advantage. 

They ensure that every point of contact on their service chain and their associates--lender, title, notary, remodel-- is extremely professional and painless as possible.