In fact, you could even collect a swab sample from one of those surfaces (choose the blackest one) and sent that sample to a lab.  

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

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?

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

until you concentrate in Mammalogy, Botany, Herpetology, or even further down into molecular biology or organic chemistry, but you have to start somewhere.   

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.

Mark is retiring from scientific/chemistry work.

Here in OC, it's not even possible to find a 100K SFR, and if you did, it would be in a terrible terrible location, probably a combination of being in the most crime ridden neighborhood next to the biggest freeway with no sound barrier, previously a meth lab, etc etc.

Someone who does 30+ transactions a year and you have a good chemistry with.