Hi We purchased a property last year, a tenant living in one of the apt was cleaning the building for the previous owner, and got $50 off her $650 monthly rent.

It kept him involved and committed because he had money coming when we sold the property.

I've been involved in this type of process a few times feel free to reach out.

Unless you accept a cleaning deposit. 

There plenty of other opportunities elsewhere, my clients are involved in institutional grade properties across the country.

So it would probably be in your best interest to wait until the lease ends and let the renters know that you will not be renewing their lease so that it can get fully cleaned and ready for showings so that you can get the highest offers.

Practically, when you seek to turn the unit, do your best to move into one room or the garage (if garage water/weather tight and no electronics in cold winter) and clean the unit and re-rent. 

If you have vents in the floor you need to have them cleaned and or replaced as well.

There isn't one right answer to that question--it will be a negotiation and is dependent on context and the relationship involved. 

Very profitable for all involved.