I just can't see rats in a 900k neighborhood, but maybe with California's insane priced-out market 900k is a rat-infested neighborhood!

My properties are located in a drug infested ghetto.

I chatted with the pest control guy who says some of the class A places he services have that issue along with pest issues.

Also, the friend may not report problems with the property because they don't want to "be a pest" therefore causing some deferred maintenance.

That reduces possibility of interior pests.

This is the first month that there excuse holds any weight, the home became infested with bedbugs which cost them around 600$ to treat. 

Also, pests love dirty rentals so you can reference that as well.You don't want to perform these all on the same day or time of month either.

Otherwise, they will start manufacturing supposed mold issues or pest issues, and they may even cause damage and then say you're neglecting the property and it's uninhabitable and call the building inspector, etc.So, maybe there's a middle ground. 

Sometimes it looks good, then three months later when they move out the place is completely trashed and bug infested, as @Dennis M. noted. 

No pet food left outdoors.No bird food or bird feeders.Call a pest control company but these are main suggestion..Any garage the cars could be stored inside might help.This can also be a huge issue inside homes, the mice get in and eat the insulation on the electrical.. we had a fire in our neighborhood.. cause mice ate wires, was a newly rehabbed house on the river 459K and burnt the day before closing.. insurance covered the rehab costs.