RV parks do not honor advertised rate when booking?

No crime. Not at all unethical for your example. They did exactly what you agreed to in your contract with them. It is something you were informed of. If you dance to the tune you got to pay the fiddler.
In my years of RVing I have never had a rate increase after making a reservation. On the other hand I would not make reservations with a park that had that kind of stipulation in their rate policy.
I don't see a legitimate complaint.
Sorry. Hope you had an enjoyable stay.