I always recommend using a cruise specialist agent when booking a cruise, as they can guide you on the right line, cabin and find the best fare for your needs. However, you may find that the best fare comes from an agent in a different country to the one you live in.
I have met and corresponded with many cruisers who have got better prices by using a foreign travel agent. Although prices are managed globally in most cases by the lines, there are many occasions when people I know have saved hundreds, and even thousands, of dollars on the price of a cruise. It seems to be mostly on longer cruises such as world cruise segments or extended voyages.
You may not have to use an agent in your local market when getting quotes and making a booking. If you are looking at a longer trip, going on an expensive cruise or travelling in a luxury suite, why not get estimates from agents in other markets? First check if they are able to do a booking for you, my own agent in the United Kingdom has been able to make bookings for people in United States, Canada and Australia and save them money.