I agree with Scurvy dog book with Carnival directly and watch the rates yourself. If you book early saver rate with a TA you can not put in the early saver price drop yourself. It has to go through the travel agent.
I had no choice, I was using cruise rewards points to book so I had to use the credit card company's travel agent. We made 3 early saver requests. When I went to put in the fourth early saver request in they wanted to charge me $50 for "changing the reservation." It took a lot of calls, but the issue was worked out in a way I was happy with.
We paid $509 the price at one point dropped to $404. The price of the cruise for my cabin is now $654. I have $210 of OBC. If you book early saver yourself you need to watch the rates and put in the request at the right time. My last request hit the low of the price range. I was lucky, however, I was watching the rate almost every day. The $404 rate was only on the site 3 days then the price went up. If I was watching once a week I might have missed it.