He is syaing is consititues and threat to his health and safety and that they expect it resolved or he plans to excericse  chapter 92, subchapter B of the texas property code.I believe the correct action plan is to fix any gaps into their living space (the first time we have head about any gaps) and then let them deal with the 'rat infestation'.

Once you know the "health" of the house, the rest is just numbers. 

did he have mental health issues?

Tell you a story.. so in MA, if you give notice to tenant to vacant, immediately the tenant would go to the board of health ---- board of health even told me straight up during my call that they use this trick for years.

Like I said, you will need to investigate, zoning, city ordinances, insurance, permits/licenses, health codes (if you have anything over 4 units, with more than 1 floor, you will be under ADA compliance jurisdiction), and irate neighbors.

I remember one of my sergeants asking me if I really wanted to do this—give up the retirement, health benefits, and steady paycheck.  

On the flip side he has done little to nothing for me and I get these sob stories that the sellers are old and in bad health and so they need the money.

How about this lets control health care .

My biggest obstacles are:1) Fear and uncertainty (corporate work provides a steady and known income, Health Ins, etc, what if I lose all my money?)

Neither the Seller’s and/or Buyer's business shall provide fringe benefits, including health insurance benefits, paid vacation, or any other employee benefit, for the benefit of the Consultant under this Agreement.6.