I've been investing in the Detroit market for years and the returns are very attractive.  

So a sale with owner financing might be attractive to him.But @Gregory Hiban's suggestion was probably the one that gets him where he wants to be. 

The properties seem to be a little less attractive and often times even home made looking.

You will get more value 20K min with a more attractive garage such your home stands out.

It will help with liability, makes the unit more attractive with natural light, and will make your property more desirable when you sell. 

There's lots of things that impact a short-term rental's performance and value that won't fit into that calculator, such as how many it will accommodate, does it have a view, proximity to attractions, are the roads difficult, etc.  

I can't control how clean they live so I can't control them attracting pests.

Pricing is not very attractive in my area.

I was afraid to look at homes below market value in my area thinking that they would not attract a buyer.

I want to rebuild homes, update them and get people living in better conditions, overall bettering the neighborhoods and attract businesses.