There were a few bumps along the way, like them subleasing a room to a guy who turned the room into a meth lab. 

You are just guessing, unless u sent samples to a lab. 

Chemistry is not a matter of opinion.

A lot of chemistry involved.

We always test the water when a well is involved, most water testing labs have a selection of tests from very basic to sophisticated, almost like a Chinese menu.

However, you have to mail it out to a lab and get it tested...

Lab report came back 65 raw ct of Chaetomium, 7,200 per m3 in the garage.  

Had a meth lab, a few overdoses, had a machete fight in one of my rentals, and other crazy things.

The inspection resulted in no mold and the air quality lab results came back normal.

Inheriting tenants is not up there on my wish list.Never let the seller talk you into keeping someone on, it may be more to their advantage than yours.Seems you have inherited a nightmare tenant.Couple of things are outright concerning here:1.I never allow tenants to change locks and I will always have a copy of the key to be able to get into the unit as needed.I do however work to provide notice when feasible, not always possible in the event of an emergency but this is also detailed in the lease agreement;2.The mold defense is one if not careful tenants will try to use against you.Closing on a house where the existing tenant (that we are inheriting……yes, I know, I know, I had to keep one to avoid double vacancies) reported mold.I insisted that we do a test before closing as I did not want to take on that liability.No mold found and we have the professional report from mold testing lab and inspector;3.Prior evictions?