In my case I did not rent to a "professional squatter" but I ended up with one. My tenant, a single male truck driver in his late 20's, was a great tenant. He always paid his rent on time, kept the place in working order, didn't whine, etc...
Two years into his tenancy he started dating a girl. We live fairly close and would drive by the place on occasion, nothing ever looked out of sorts. She slowly weaseled her way in by staying the night occasionally when he was home, then "taking care of things" while he wasn't home. Eventually she started having her medical bills sent there (established residency) which he didn't know until he saw them in the mailbox. She then took up permanent residence (without my permission as stated in the lease) which I was not aware of until I receive a phone call that my tenant had a restraining order against him and was not allowed on the property!
He had paid the rent and 2 days later she came in already beat up (according to the neighbors) and called the police saying he did it. They arrested him on domestic violence charges and placed a restraining order against him. Since she had established residence at the property (with the mail) he was not allowed near the property even though he was the only one I had a contract with! In the end I found out that she had done this exact same thing (according to police and court records) 4 times in the last 5 years. She lived on my property for 3 months while I had to file eviction on the actual tenant and name her as an "unknown occupant" because I didn't know who she was or the other several people she had taking up house there.
I have found that the law is not on the side of honest people in most cases. She knew exactly how long she could stay and even told the neighbors the procedure! So I have learned that even good tenants can make poor choices and there is not a dang thing you can do to avoid it at times.
