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?

First qualified person that give a deposit gets the place. 

Currently my hot tub maintenance person says I need to schedule her to come out to the property after every turnover to poor chemicals in and clean the tub.

So, you should either join a local investment group where you can ask questions and learn from more experienced DIY landlords or be disciplined enough to search here on BP and the internet in general to learn what you need to know.

@Amy Lin - If it were me I would have an experienced attorney start the eviction process immediately.They are probably going to hang on as long as they can rent free as they have the closing proceeds.They might care about their credit if they do plan on buying another place, so you might have some leverage there.

and include my tenant's name and this unknown person? 

If you decide to entertain this, due diligence will involve digging deep into the business financials to understand cashflow, solvency, and liquidity, his personal finances, and searching for any liens or UCCs in place. 

@John Guillory I personally believe that its the way in which you are presenting yourself when you talk directly with the homeowners that gives the "shady" terminology.

DSCR loans offer alternatives for DTI/income and employment, but generally still have strict personal credit requirements. 

Learning about the seller's approach and way of thinking can help you make your negotiation plan more effective.Every seller in the real estate market is different, just like every person is different.