When you're looking for an agent, just don't look for a general travel agent. You also want one who is a Cruise Specialist. Ask alot of questions; how long have they been doing it? How many clients do they have? How many cruises have they been on? What cruise lines have they cruised with? Where have they cruised? Etc, etc.
Check out their website; is it professional looking? It is a cookie-cutter website with no personal information on it?
It's like finding a person in any profession - you want somebody you feel comfortable with, somebody who cares about you, somebody who is not in a hurry and takes time to answer all your questions, somebody who is readily available when you need them and responds back to you in a timely manner, and somebody who asks you questions so they can help you find the perfect cruise for you. And stay away from agents who are always 'recommending' things. Remember, we're different people and we like different things, so what one person lovers, another will hate. A good agent will provide you as much information as you can handle so you can make an informed decision on what's best for you.