The blood spatter on the walls and floor?

As for AirBnb itself - they are far easier to work with and get the hang up than VRBO. 

Mainly I’m trying to avoid “aged poorly design” glassblock walls, small bedrooms, older windows (wood/aluminum, single pane), aluminum patio covers, and to a lesser extent landscaping.

Replaced both toilets with brand new ones, replaced the 2 car- garage door with a brand new one, had all the walls freshly painted, put brand new baseboards in, and had the kitchen cabinets painted as well.

If you can reasonably throw up a new wall and closet, turning a 3 bed into a 4 bed, that is a great place to start, but only if it works for the property and you have at least 2 full bathrooms.  

For instance, one property seems to have an extra bathroom that is not listed in the county records.I plan to make some modifications, including removing a closet wall to expand a bathroom and taking out a kitchen island that contains electrical outlets and a switch.

It could even be impossible....Some inspectors will insist that walls be opened to view wiring/framing/plumbing/etc, floors be jackhammered up to show vapor barrier and rebar spacing.Ask me how I know........

For example if you asked him to only paint a wall but the wall does not look good because the drywall itself is bad - that is not his problem because you did not want the drywall fixed.Specify what it is you want done and if complete you will release the payment. if he disagrees then he may sue and then let the court decide. 

Hang on to it for 5 years and then sell. 

Like someone else mentioned, doing a short term rental in a secluded basement that is very private and walled off is one thing, but sharing the same refrigerator, kitchen thermostat, etc. with a complete stranger seems like it will introduce more problems than what the money is actually worth.