RV parks do not honor advertised rate when booking?

Perhaps you should check the rates prior to actually arriving at the park to see if there has been a change and then cancel if you don't approve of the higher rate.

Or you can just simply not reserve at a park that has that rate change clause.

Personally, I've never made a reservation a year in advance. I have stayed at Flying Flags and it is a wonderful park but we didn't have to book it a year in advance or even a week in advance.