I agree about using local agents. But, shop your rate out first. TA's make money on commission based on the cruise rate. Have that knowledge before you call or go in. If you find a good one that looks after your interests as they are suppose to do, stick with them.
If you know Riviera Deck Outside is selling for $449 and Empress Outside is selling for $849 and you ask for an Outside Cabin and are quoted the $849. Then you know they are not looking out for you.
As in every profession there are good people and bad people. Most Travel Agents are good people. They depend on repeat customers.