We just had an experience where we went to our local state park (about 30 miles from home). We had made a reservation for the site about a month earlier. We could have gone earlier in the day, to see if the site was vacant (Check out time is 4 PM) but we deliberately waited until about 3:15 PM to leave our house. When we got there, we drove through the campground and it was then about 5 minutes to 4 PM. The previous campers were still there, they had their boat hooked up to their RV and the site looked pretty picked up, but they were sitting in lawn chairs at the side of their RV. We figured they were waiting for their kids to come back from swimming or something and were ready to leave.
We went back to the visitor center to kill a bit of time. We talked to the Ranger who confirmed that they were to check out and we were to check in. We then went outside and waited to see them leaving the park (only one way out of the park which was by the visitor center). After waiting until 4:20, we decided we'd go back to the campground and see what the deal was. The ranger saw us getting ready to go, and he came out and said: "Let me go in front of you. I'll make sure they leave." So we waited another 5 minutes and then drove back. The ranger was parked by their campsite and was talking to them. Then he came over to us and said "They thought they had the site for one more day. They'll be gone in 5 minutes." They soon pulled out.
I am just glad that Ranger Barney took it upon himself to go on our behalf, as he was able to clear things up quickly. Thanks Ranger Barney!