For me...
1. Sometimes (well, most of the time), as I'm often on a schedule and like to be sure of a campsite when I arrive. Online reservations are usually more convenient for me than by telephone or whatever.
2. I don't care for online (or other) reservation fees, but they are a fact of life often. If you're talking about a separate additional fee to lock in a specific site vs. reserving any site in general, that's a wrinkle I have not yet encountered.
3. If no specific site, area, or need were given, I wouldn't necessarily expect to know if I had been shifted to a different site and generally would not care if that were done. If I chose a specific site to reserve, I would generally not expect that to be changed, and may have reasons for prefering the site that the system doesn't take into account; however, if called and asked, in many cases I'd be perfectly fine with being relocated.
4. If the system online gives no indication of site availability, I would probably not think on my own of calling/emailing about site availability. If some sites are marked as unavailable for reservation due to "phone reservation only" or something similar it would make it a lot clearer what's going on; even a blanket statement that not all reservable sites are available online would be a good idea.
5. Sounds reasonable.
One final general note: having specific searching/reservation criteria is nice, but it can go too far. Undergoing a survey akin to Lady Bracknell's interrogation of Jack Worthing just to get an overnight place is a bit much. At some point it might be better to present the available sites and their features/quirks and let one choose than to try to suss it out via AI.
