Besides raising rent, are there other areas where you can generate revenue (such as if its a multi-unit property added coin-op laundry, or add storage)...Other than that, unfortunately there is not much you can do.

Current market is trimming the fat, see it as an opportunity to eat market share. 

We checked the lease and its clearly stated that garage should not be used as storage and no perishable foods should be placed there

The applicants say they always paid rent in cash,  the rent receipts are in a box in storage, would take awhile to find.  ..Would you insist on talking to the most recent landlord by phone? 

As Michigan's third largest self storage facility at 117,000 square feet, we just completed 68,600 sq feet addition too this facility.

Currently a 3 bedroom looking into adding closet to what they had as storage it has a window.

Can you rent a storage unit somewhere instead?

We would boost the value through AirBnB-ing 1-2 units, increasing rents, and also using the detached garage for our own purposes -- storage, workshop, etc.

I forgot to mention that supposedly they are moving all of their stuff into a storage unit so unless they are lying I would assume that they are going to be moving in with family or friends until they can find a place.

In my case, I have residential rentals in one LLC, commercial properties in another, self storage in a third, and my real estate company operates in a fourth.