I've had to evict tenants and it isn't fun. It always involved the police. As for AirBnB guests who won't leave, they are trespassing and calling the police is normally your only option. The good part of that is if there is a question of whether or not you are the host, you can show the listing with your picture on it.
I've had guests holdover before, and all I can say is you have to go with your gut on what you think the outcome will be if you do or do not call the police. If I have a same-day turnover, I just go into the unit at five minutes past checkout and tell them they need to go. I then give them up to one hour past checkout, depending on how much cleaning the place needs. By then it should be apparent if they plan to refuse to leave and the decision on the police becomes easy.
