If they are a pain in the neck and never pay on time, I would try to do cash for keys, offering 1/2 rent and telling them to move out in 1 week or 2 because my niece is moving in in two weeks.

Unless you will begin seeking other funding such as hard money lenders which can be a bit of a pain.

I think running your numbers and setting your goals is your best bet.I would stay away from condos, the condo boards can be a pain the neck.

How do you deal with people that are never happy with what they have and are pain in the A$$ to deal with?  

It can be a pain to maintain the property's appearance to historic standards, and it is almost always way more expensive.

People who bought and hold aggressively between 2009 until now are doing very well, but if the market flatten out or go negative & your strategy depends on equity gain, you will be in a world of pain.

@John Baker, what I mean is that as an investor your business card just as all of your marketing should promote what you do; help alleviate pain from home owners with distressed properties. 

Being a landlord is a pain in the butt.  

my son has a neurological illness that throws him into excruciating pain.

You may be able to get some history with name and birthdate and maybe a driver's license number but my immediate thoughts are that they are either hiding something or extremely paranoid, either way they are going to be a pain in the butt.I will not enter into a fiscal contract with and rent to anyone that I cannot verify who they are and do my due diligence on.