Here at PA State Parks the camp host puts up the reservation tags on arrival dates in the am and removes old tags.
If the site is reserved and tagged, it's NOT available, regardless of occupancy. If they paid for it, it's theirs.
We've had a favorite site unavailable and unoccupied.
We've also been on the other end when we reserved beginning on Wed, but our daughter was quite sick, so we came in Thurs eve. Of course, we called the park to let them know.
When we leave, we usually make a swing past the host, let them know we're leaving (so early arrivers can take the site if they want), and often leave firewood for the next guy- or the host.
That way no one worries that they are taking firewood from a "still occupied" site or whatnot.
We also invite the hosts over for at least one meal during our stay. It's neighborly and shows our appreciation for everything they do. It's usually during the week when things are slow at the CGs.