In most commercial loans, the guarantee applies based on a "bad boy clause" - which would mean some sort of criminal activity. 

Did you run a credit and criminal report?

No criminal background.He has his own electric company so he his self-employed with 6-figure annual income.

I am a lawyer (a criminal lawyer) who not so long ago practiced real estate law.

You probably mean quitclaim, which should cause you concern if you are throwing out incorrect made up terms you've never used or heard of before.Putting yourself on the deed may be a criminal offense depending on the lie promise you tell to the homeowner, and/or, may subject you to licensure/registration from the state."

Hopefully you do a criminal background check as well as credit?

He does not have a criminal record.

.), along with a report that covers criminal, credit, and eviction history.

Advise that you have sent a Notice To Quit and you would like to have the occupants charged with Trespass/Criminal Mischief.3. 

Here's one nightmare scenario:Adult children move in without signing a lease or undergoing any screening or verificationCurrent on-lease tenant suddenly moves outThe "temporary situation" ends up lasting a year or moreNow you've got two unknown entities living in your property: no SSN, no credit check, no criminal background check, no rent verificationNope...Every (EVERY!)