I work with a few other organizations that offer certifications, one thing I find that helps in studying is a sample test. It gives a learner some relief from test anxiety AND a way to see not only what topics they think they need to study, but what the people making the test think they need to study.
In short… people hate to spend 400 bucks ( or ask their boss to spend 400 bucks) only to fail on their first attempt because they thought they were ready.