The best advice is what Cruise Fanatic gave.
Agreed. I always refer people to the CLIA site, as well. From what I understand, the requirements to earn the various CLIA certifications are very rigorous, including seminars, courses, exams, ship inspections, and taking cruises themselves.
As for my own situation, I use a TA who is an Elite Cruise Counselor through CLIA and who works from her home. I heard of her the old-fashioned way...word of mouth. She and I have worked together for six years. Prior to that, I used another home-based agent until she retired, and then tried some local and Internet options.
Keep in mind that no one method is right for everyone.
Something else to consider is the advice a TA can give you regarding your destinations. This isn't as important if you are going to the Caribbean for the 10th time (for example), yet I found it critical when starting to explore Europe.
Good luck in your search!