I hope Sandy will respond, since I know she is an MCC and has been for many years.
In a nutshell, CLIA (Cruise Lines International Association) which is an accrediting organization for professional agents has a program for becoming first an ACC (accredited cruise counselor) and then MCC. This involves completing various training courses, doing X number of cruises, and doing inspection tours of X number of cruise ships. It isn't easy and you have to be a CLIA member and an agent. The average person on the street doesn't qualify.