Can't you claim that since they are no longer renting the room (as they do not have it reserved) they are now trespassing on private property and get the cops to boot them out?
Yep, you can. Unless they've stayed for 30+ consecutive days; then (at least in WA State), they are considered a permanent resident and have more tenant's rights, and it becomes a pain at that point. If this SC after only one night hadn't moved, though, I could have called the police. (And in the past, have with others.)