Visible dirt/dust on almost every surface, trash (including Q-tips) left on bathroom floor, toilet not cleaned, food splatter around kitchen, smudges on walls, windows and mirrors, list goes on... 

As you're managing longer leases and not worrying about toilets and trash. 

A clogged toilet that's caused by constantly flushing down wipes?

Then you can collect monthly checks and not deal with clogged toilets.

How would i handle her doubts about squatting rights?

Updates include new upstairs flooring, kitchen counters/sink, bathroom vanities/toilets, and fresh paint.

The area I am targeting is a vacation destination that is rather seasonally resilient (working theory backed by decent to moderate research so far).If I can get past the zoning hurdle specific to mainly "wastewater" - referring to the collection of the toilet, shower, and sinks discharge - I want to purchase 10+ acres that allow me to scale to something quite significant in time. 

I’m wondering how common of a problem squatting is in the Cleveland area, and what strategies can be used to minimize the chances of it happening.

I want passive mail box money not tenants toilets and termites

This is the simplest method, but it also means your tenants are more likely to abuse the utilities by leaving windows open with the heat or A/C running, leaving lights on, ignoring the toilet that constantly flushes on its own, etc.3.