It's common for a tenant to get a "prescription" or even multiple prescriptions so they can register all their pets as ESAs but I don't accept that.You have to decide where you are willing to put your foot down.

You would find boarded up buildings, graffiti everywhere and drugs being dealt wide open in the street.

Death, divorce, disinterest, default, drug-use, etc.  

What if it turns out they have a serious issue like a sex offender or felony drug issue in the last year. 

It isn't only about the relationship with the x-girlfriend but also is he really paranoid or do drugs play a role.

You should also give him an idea of where you need the budget to come in at.I use a lot of contractors in my day job, this guy sounds like a fly-by-night operation, hard up for money, drugs, etc.

We also suspect him of having dealt drugs, not that we can prove it.Awesome!

Many people who squat have drug problems and meth and crack make people do things they would not do sober.

Very tough to screen for a non-drug/substance abuser who starts work at 8am.  

Drugs, crime, abject poverty, etc.