I have been on a few cruises booked through a travel agent and I have picked my choice of cabin at the time of booking. My understanding is that once my booking is confirmed, then my cabin will not change. Why should it?
So my question is: what is a guaranteed cabin? And secondly, why would you want to go through all that hassle of changing your cabin when you get to the ship? I know that I can't wait to get on board, kick off my shoes and unpack!
I can tell you, that it takes me years to save up enough money to take a cruise. By the time you figure in airfare from Canada as well as the cost of the cruise, I feel very fortunate to be able to book a nice balcony cabin.
Maybe people shouldn't be so greedy and just be thankful that they can afford the trip.