I would have him sign a Disclosure of all aspects of the transaction, in front of an attorney that they know they are selling the house, that they know your intention is to make a profit, that they are not drunk or on drugs while they sign this, etc, etc, etc.

If you are on your own well water, talk to your plumbing supply house about plumbers that specialize in water treatment systems that could come out and check your water.

They've been in the living situation with family for 5 years and had an 8 month stint away where the male and female adults lived in a sober living house after she was convicted for drug possession.

Ridgecrest (California) is by far the worst city for landlords,but it is not because of their policies:-)in 3 years of owning and managing units in RC, I saw - drug labs, neighbor tenant murder, police chased and shot and many other various situations.try to pay tenants deposit back to them after going through all of  this.NOT funny

No special treatment for RE pro  in CA. 

We soon discovered the small rental kitty-corner from us had a drug issue. 

@Carson SweezyA primary residence is specifically excluded from 1031 treatment.

IMO, there's no one best election, which is why I have multiple series w/ different IRS statuses, and perform the activities in the entities where I get the most favorable tax treatment.

We have terminated month to month leases on tenants that were paying in full on time because they were not good tenants for other reasons (drugs, etc). 

Off the top of my head and keeping in mind that we all have standards that may not be strictly legal would you reject some of these :Neck and facial tattoos, single guys, recently separated women, single mothers, welfare, restaurant workers, nationalities know to cook offensive smelling food, smokers, low income immigrants, bikers, tattoo artists, recreational drug users, prostitutes. others.Or based on human rights laws etc. is everyone welcome as long as they pass basic screening standards.