Based on past performance and current economic conditions, I have decided to diversify into real estate.

Now of course, you have different classes of apartments in different locations which have an influence on the type of good it would be considered (ie college apartments, blue collar/working class, upscale, etc) Normal goods in my book to name a few would be retail centers (which typically take huge hits with economic downturns, especially without large anchor tenants), smaller or single tenant office properties, and warehouse/industrial properties (with highly leveraged tenants with tight margins running on leveraged A/R and inventory). 

Is that physical vacancy or economic vacancy?  

I found three 4 unit properties that are 80% occupied being sold by an individual in declining health at 86 yrs old.

Figure out the economics and you'll make a LOT of money. 

I was told that there is nothing in Fl. law that prohibits these tanks, but any leakage violates state & federal health statutes.

However, in C/C- areas, and as a rule of thumb, expenses are always higher and income lower due to vacancy/economic vacancy.What is the city/state? 

Demographics, economic trending, CMA'S etc.

And we all know that the first rule for preserving one's mental health and faith in humanity in our modern world is "don't read the comments section!"

Overgrowth and rodents are safety, fire and health hazards, and most cities have ordinances governing these.