Paint walls, make sure everything is in great condition.  

But when you’re intimate with the property, you know exactly what’s going on behind the walls, under the floors, and in the systems.For example, a seller might tell you, “This property has a ton of equity.”

Tons of double sided tape used which results in a fair amount of extra effort to restore (most cases paint comes right off the wall requiring patching sanding etc, some cases Good-off was effective.

The 4 guests smoked marijuana in the house (strong smell), broke a window blind and a picture, put a hole in the bathroom wall, chipped an end table and worst of all vomited on the couch and front porch.

I'm also thinking of turning a room downstairs into a bedroom with a simple wall.

Typically they have a side entrance that leads to the basement which can be easily split up with a door/wall.

My current tenant has removed a picture from the wall and replaced the provided bedding with their own belongings. 

Investors focus on adding Accessory Dwelling Units (ADUs) to increase income streams.

For example for a few holes in the walls they have someone paint an entire unit and take their spread.

There are tests you can buy on Amazon, where you can swipe it on the walls to determine residue.