pitch, we had the opposite experience in Great Basin Nat Park. On a rainy day (key fact), we spotted a totally vacant site that was first come, first served. We set up our trailer.
After a half hour of work, a guy shows up in a panel truck, claiming that this was his site! It turns out that he had posted his little ticket stub on the stake in front of the campsite but that the rain had washed it off the stake and onto the ground. When we found it, there was his name and date.
He had failed to leave any evidence of occupation in his site -- when we asked him why, he told us that he had no excess possessions and had to pack everything up when he drove his truck from the campsite to the visitors' center.
So we had to leave. Moral of the story: even if you think the site is vacant, check carefully for those ticket stubs!!
