If they're only willing to pay by check, it could be a red flag in my opinion. 

Do you go to conferences, yes, but when I see their ads for their courses, books etc. to me that is a HUGE red flag.

She would have money for Aug rent, if not red flags because what was she going to do if she stayed.Her leaving on the 20th means you have some time to go in and clean it up (probably not much to do as she was there for 4 months) and maybe get it rented by Aug 15.

There are facebook groups just for RAL Managers, so get in contact with some of the members and see if the person has any red flags.

As many others have recommended, I would definitely do some deep research into an area to understand what housing rates and property taxes look like in the areas you are interested in.

But with all the red tape, why would you want to?

"High demand area" and "off market deal" are red flags for newbies!

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?

Insurance red flags.  

 @Stuart Udis:OK, yes new investors- not deep pockets.