This may require personal attention; a PM or contractor usually lack the drive to finish the job compared to the owner. also clean up the outside, fertilize the lawn, clean up the edges, make sure the garbage area and hallways are spotless. 

I think this can work when targeted to a higher net income niche of people who don't want to clean up after themselves nor work-out how to be a household- Barcelona, San Fran, & London are excellent locals for this. 

You could also present an environmental argument in that my homes are occupied by people who otherwise would have to drive longer distances to work, thus increasing pollution & resource depletion.

And I don’t just mean an easy cleanup and touch up.

Clean up the landscaping outside.

I would not invest in townhouses or condos, they will deplete any potential strong cashflow.

Not a fun cleanup..

Sent them a notice that they had to clean up all of their lease violations and notified them that they can either renew the lease with a rent increase, or vacate.

Asset Depletion loans may be a viable option for you as well, but they will not provide low, comparable rates to conventional. 

These can be obtained well below potential sale value after upgrades and clean up.