I worked in the hotel industry fro about 15 years. We could not throw out a compliant and paying guest. However, if someone was over-staying their booked reservation (and we needed the room because of full occupancy), we would inform the guest that their rate would default to the rack rate. As the rate on their reservation was only legally valid for the duration of the booked reservation. That would usually persuade them to begin packing up their belongings.

On the other hand, if they still remained and we had to "walk" a new guest because of it, we at least would capture a high amount from their rack room rate to cover the cost of the walk.