I was also told the bank would reimburse me during an investigation (never had to push them on this). 

I would see about the cost to get another meter or to investigate some of the non utility sub metering options that are available, you may find the House is wired in a way that makes it impossible to sub meter.

This gives a landlord limited freedoms to within reason investigate the ESA.   

As I investigate, estimates are 10% of houses sold have greater than the limit of 1 / 100cm2, and as high as 40% of all rentals nationwide have borderline or higher traces of Meth in them.

If it’s a crime scene there may be issues with entering as we had to wait for the police to finish their investigation

these are all things that need to be investigated.

If a county clerk made that statement, then maybe you should investigate and see if and how it pertains to your and your "commercial interest".

I had a plumber go investigate it.

HUD is required to be a non-bias third party and investigate any and all claims.  

Property taxes and insurance premiums vary way to much in different states for it to make sense to me to use it.If you're asking about what kind of rule of thumb to use to determine if a property is worth further investigation, I personally use the GRM (gross rent multiplier) rule of thumb, because that's what I was taught.