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What are some resources or websites to find great cleaning crews for STR?

If you can clean up some old balances that are hanging out there bringing you down, those would be the first I would go after.

It is basically a person who does cleaning, maintenance and talks to the guest while they're at the property for you.

One thing to do to try and extend the life is to keep the guts free of lint, dirt, debris, and build-up when i'm in for routine maintenance and turn-over cleaning. 

With plenty (90 days or more with an initial "head's up") of notice, I first "non-renewed", then moved out the undesirables, then made sure the vacant units were clean and functional, not doing any upgrades. 

I would go into FB cleaning groups to find your cleaners as they are more reliable on there from my team's prior experience. 

I charge a commission on the reservation only, while the owners get the remainder of the reservation + cleaning fee and I remit the sales tax on their behalf.

I was thinking of possibly offering a unit cleaning service for interested tenants as a way to create additional income and cover the cost of common space cleaning.

And as long as you've invested time in building systems and having some type of eyes on the ground (for example, in NH, my neighbor cleans and takes care of snow removal), it's a couple hours each week at most for the majority of guests.