Sometimes it has to be zoned properly or it might need to be a specific distance from an already licensed home.Then you need to determine the licensing requirements and see if you can meet those.

They never see the card.

I have their business cards, but haven’t used their BLOCs.  

You can find 1%+ rule deals just about anywhere in Detroit proper but that doesn't mean you should be buying them all. 

Take ownership of your mistake and learn to do the proper due diligence recommended above😊

In a properly run platform, VRBO would require hosts to upload this information to the platform, and the guests would access the information directly from the platform, eliminating drama. 

They could be here legally (visa, whatever) and waiting for their green card.

They might be great, but we were only 9 minutes in before the conversations turned to "what credit card are you going to use."

I don’t know the condition of the property nor how to properly assess it considering my lack of experience – who would I approach due diligence?

When dealing with unique properties like this, I would make sure that the ADU on this property is properly zoned.