I then finished my Master's Degree in Forensic Psychology in about 18 months. 

As @Thomas S. noted, most of these complaints are frivolous, but your state board has to investigate every one - and this is one case where the accused is presumed guilty until proven innocent.

You should have investigated this during your due diligence period before buying the land. 

I have paid a private investigator to find the first heir to properties before and had some great deals out of it.

It all sounds high to me but I’m here to learn..so it’s something for me to investigate.

This allows me to see what properties produce Return to Senders and investigate that further without burning up too much of my marketing budget with more costly pieces like letters.

They determine the mold is due to; (1) tenants causing crazy high humidity basement humidity by running the dryer without ever cleaning out the lint trap and (2) not cleaning the bathroom- All mold is abated with bleach, a second dehumidifier is placed in the basement, carpets are lifted, trim is replaced, and we investigated behind walls.

I wanted to clear a few things in case It happens again.In a deal like this, how do you guys deal with the HOA, meaning, do you investigate about active/potential special assessments?

It is worth investigating. 

Verifying work and references is crucial, and do your investigative work to determine if the person is good or not!