I thoroughly enjoyed your article, well-written, flow was solid, and you had more than enough to say.
I do agree with your clues but I would also say there are plenty of people who allow full access to everything, family, friends, social media, phone, moving in, etc., and still cheat. Those are the more obvious clues but it's always the hidden ones that can be just as disconcerting.
Sometimes I think it all comes down to that gut feeling. We know when somethings wrong.