From Vernon Howard’s “Secrets of Higher Success”

How can you check the credentials of a teacher? There is only one
way. We must have at least a single ray of light in ourselves, for
it is that light which reveals the authenticity of a teacher. People
without this light would ask Christ whether he had a college degree
in psychology, or ask Buddha whether he had read the latest theories
of a noted professor of sociology. Some day you may meet a man who
knows what he is talking about. To make sure you don’t walk right
past him without sensing his trueness, brighten your own light right
now.”

 Secrets for Higher Success, p. 146