Depends on park rules that were in writing at the time you booked. Months in advance I booked a stay at Flying Flags in Buellton, CA. Booked and paid in advance as required at a great low rate. Months later arrived and checked in. Was told I had to pay another $100 for my stay as the rates changed since I booked. Website I booked on did have a note that stated rates may change at any time without notice. Had no choice but I tend to think its not ethical nor common in the industry. Ever book a hotel at an advertised rate then charged more at check in? I haven't.