I want to give them the benefit of the doubt they are just struggling with staffing but now have seen some red flags that lead me to believe there might also be some type of deceit/fraud and possible financial trouble.

Donating money to large (FEMA, Red Cross), local organizations or Go Fund Me pages would be the quickest way.

I don't really want to invest in a D-class area.Tangentially, what are some of your "it's time to sell this property" red lines when it comes to the changing economic conditions of an area? 

FD came and red tagged the outlet.

On the other hand if they are a sponsor that is experienced in stopping a skin in the game, that's a huge red flag for me.c) how open to scrutiny are they?

Knowingly buying into the red just because of financing terms is a very unhealthy way to invest.

We've only had one resident fail to pay rent, and it was someone who had all the usual red flags, but she also had a sick kid. 

The fact that their documentation is not clear and they are in a hurry to move is a big red flag.

The only slight red flag was that they only accepted payment via Venmo or wire transfer, but that's how I accepted payment when I was selling lead bundles, so I still thought it was worth a shot.

These are business purpose loans so there isn't any sort of red tape when purchasing multiple properties at once or one after another.