One May morning, years ago, my girlfriend and I paid for a site at Wawona. We displayed our receipt at the site, but didn't have any cheap gear to leave out for potential theft. We went off day hiking in Yosemite Valley and returned that evening. So the assumption that if there isn't anything left out during the day that the site is going unused that night is mistaken, but not unheard of. When we got back to our campsite it was occupied by a strange car and tent.
Soooo. What was the end result?
Same trip to French Camp as mentioned above I paid for the night about 10:30; left a 12 pack of Seltzer water on the picnic table seat in plain view and firewood by the pit; put up the paid ticket on the post and drove to Mammoth to fish for the day. I came back about 4:30; my ticket was gone off the post and the seltzer was gone. Nobody commandeered the site but it felt real odd. My ace in the hole w/b that my check with all my info would be in the drop box which I placed in the box, would trump whoever else would have made the move into the spot. Turned out it was one of the hosts thought it was abandoned....Apologized the next day profusely. Never had anything like it before happen. I explained to another one of the hosts the next day and upped my stay for two more days,
Last year at Rock Creek Lake there were quite a few thefts of some expensive equipment from campsites; but they caught the guys later in the summer. For the most part people are good and like minded.I'm vigilant and look out for my neighbors in adjacent camps even though I may not introduce myself directly; but know who belongs there.