One hand washing the other.

It will probably take another year or two to wash all the failing newbies (that paid too much) out of the market, but it is already occurring.

Tyler also points out the big challenge, getting someone to do the cleaning, linen changing, towel washing, etc.  

In my experience if the washer and dryer circuits are tied to a particular unit, it's very likely the hot water supply to the washer is also coming from the water heater of that unit, so even you are paying for water, the unit tenant is paying for the electric or gas to heat the water if someone does a hot or warm wash.

Get good quality sheets that will stand up to all the washing.

I personally, I think, the biggest factors to focus on when it comes to reducing turnovers besides location is providing amenities like in house wash/dry and private parking.

Why do I need to change a tire myself or wash dishes or mow the lawn?  

This will allow you to wash rinse repeat with the Brrrr method to accumulate properties. 

When my sewer exploded at my property all that needed to happen was wash the floors down, soak them in bleach and fix the pipe.

Think STRs, Car Washes, Industrial, Etc...