Personally I want my agent working for me, rather than working for the cruise line I'm buying from.
But, technically, the agent is not working for you. He/she is working for themselves! I think their commission is always going to be their main objective.
I have to say though, I am surprised to see that an independent travel agent will get you better prices than a Carnival Personal Vacation Planner. I was thinking I got the best deal thru them.