Awesome Colin, thats amazing and very encouraging, I am not remotely where  you are in regard to business but I took risk  a in 2013 and went on my own and you are correct, so many doubting, warned, and discouraged me. 

So, short of filing a lawsuit, would it be fruitful (and help warn other investors) if I:- Submitted a complaint to the Better Business Bureau?

You may want to get an attorney and hope RTR doesn't sue you.There are numerous posts here on BP with warnings about buying turnkey because you pay top dollar.

It's as Buffest warned, the greatest transfer of wealth in human history in action. 

In the 2 months since, they've warned the ex-tenants multiple times over email that they'll be sent to collection if they don't pay, and they haven't.

Is this accurate, if a property is owned by investors and constantly being sold and bought that's a warning sign? 

There is a lot of grey area on this site, as there is on most sites, and in the interest of wanting to be fair to posters and not be ridiculously heavy handed, most mods will give posters the benefit of the doubt on the front end, maybe with removing a post and a warning or something similar.

We also have a stern conversation with them about not hiring vendors and that they would be fully responsible next time.

Give a written warning and demand they correct the violation within X days.

The only problem is, they seem to be very lazy and inconsistent (just irresponsible all around) - in the past when I've had to send them warnings (short of an actual 3-day notice), they do mitigate the most important issues but only half-assed and temporarily.