If the property is without rent for months and your pool of tenants is almost nonexistent (which is what it sounds like), then you have to evaluate the root cause of that.

I'd charge a holding deposit and collect it so that if they back out you have something for your lost time.I give my applicants less consideration if they are moving from out of the area since they are less likely to stay long if they don't have roots, but I have found that in my area and probably isn't prevalent.  

Ferreting out the person behind something like that is John's job, but even most shysters won't put in the time / effort it takes to pierce multiple corporate veils, find the trust at the root of the structure, then make the paper chase to find the protected (non-public) information which would lead to a person who may or may not be in control of the entities and their activities.

Maybe set down roots?"  

We're rooting for you!

I wasn’t born in the south, but I do have southern roots... so I’m able to slip in and out the dialect as necessary.

I never root against the home team.  

Most use what's called a Veeder-Root system for that.There are/were quite a few single-wall stainless tanks in use. 

They also had a camera showing roots growing into the pipes, etc., etc.We hired another plumber who simply snaked it again, located the drain clean-out, we talked to the tenants about not putting grease down the drain, and that was the end of it. 

Do a quick search of "how many people didn't pay their rent" and you will see links to articles on the first page stating anywhere from 4% to 40% didn't pay.The rooting-for-disaster NY Times says that 31% of people didn't pay rent by the 5th of April of this year.