The owners can hire contractors that will go to the property in order to help 'determine the conditions' under which the squatters will leave. My understanding is that it's usually a balance of physical intimidation and financial incentive.
I have seen this happen with a building across the street from where I lived. There were 5 large men who could have easily been bouncers in Oakland outside with "FueraOkupa" shirts. The woman left later that day.