I've printed out a Notice to Quit and will post it on their door for legal protection.

By recognizing the signs and implementing effective preventative measures, landlords and property managers can protect themselves from potential scams.

And, the longer you wait to act, the longer the squatter stays - and even gains some legal protections to stay while your waiting on a slow court system to act on an eviction. 

The later is critical to protect your investment.

In the NE states, AKA tenant friendly states, I would always have a PM to help protect my interests.

A well written management contract should clearly spell out what is expected of both the PMC and the owner, to PROTECT both and avoid misunderstandings.

An emergency fund needs to be liquid, and immediately available to you in addition to being low risk and protecting principle. 

There are thousands of pages on consumer protection laws and regulations that depending how you go about doing a subject to could be against these laws and regulations. so like most things - is itillegal - it depends.  

A well written management contract should clearly spell out what is expected of both the PMC and the owner, to PROTECT both and avoid misunderstandings.

Figure out ways to enforce rules to protect yourself and the other renters.