We have never had someone not leave on time, we did have someone on our site because they liked it better and just took the already registered to us site. We did not say anything to them and let the campground managers deal with it. The people were very nasty, we stayed out of the way while they moved.
Another time check-out time was 1:00. We decided that morning that we would leave around 12:30. Around 10:00 a vehicle and camper parked on the road in front of our site. They asked us when we were leaving. When we told them, they said we needed to leave because they were ready for our site. We told them we were sorry and went for our bike ride. They got their chairs out and just sat facing our camper. I think we ended up leaving around 11:30. I just got tired of all their drama.