When I was CG host I made it a point to be sure campers knew when the site was booked for the night they where scheduled to leave. Mostly just the reserved sign on post. If I saw somebody was checking in on a site that was reserved for the night they planned to leave I would offer to move to another site that more likely to be able to extend their stay if wanted.
Somebody get there early? If the site is MT, set up if you want. But because you are early I might not have had time to check the site. You loose your right to witch if there is trash left.