Both are now completed thankfully for persistence.

Since this guy is persistent, the first thing that comes to mind is that you don't want to be reported as being discriminatory (if that applies). 

They persist even when I explain that if they can't speak English they can't sign the lease.

The lease should stipulate the the tenant is responsible for taking care of any accumulation of moisture and required to notify the landlord in writing if the problem persists.

Finding the opportunity isn't obvious or free, per se, but there's no reason you can't leverage your networking or dogged persistence to do it.Money, Opportunity, and Execution form the triad of a successful investment. 

Why do you persist in keeping bad tenants in your houses? 

I was unaware that the situation had supposedly persisted until now.

I admire your persistence and not giving up and holding your property as long as you have.

If he tells you that there are no bedbugs, which is damned hard to determine with any degree of certainty, then you find the infestation persists, he could be held accountable for your problem.You might talk to the inspector to determine if this is his real issue.

In the end, we would rather have someone called pre-maturely than a potentially damaging (i.e. overflowing toilet) situation persist.