On the subject of experts, there is a modern-day variation on the idea of an expert that many people might possibly not be aware of, called the "thought leader". I think the term got invented about 15 years ago, and before that such people might possibly have been described as "gurus".
I was reminded of this thought leader thing on a recent visit to Matt Briggs' blog, where he has written a humorous blog post a few weeks ago mocking the idea:
As I understand it, the differences between a thought leader and the traditional expert are that the thought leader always has a strong media presence, is using the idea of being some sort of expert as a marketing strategy, can be a company as well as an individual, tends to be a pretty high-up individual in an organisation, and can afford to get things wrong as the media will still come back to them as being one of the "go to" people on that subject. The thought leader may also possibly not own a briefcase. The traditional expert is often unknown by the media, is pretty low down in the pecking order of an organisation, and is likely to have their reputation damaged by getting something wrong, as well as owning a briefcase.
The Green movement seems to me to have made a lot of use of these thought leader-type people over the years and may have even invented the idea, with the business community adopting it later. The first one I really noticed was Paul Ehrlich (author of "The Population Bomb" book in 196 . I was intrigued by the fact that Ehrlich was being portrayed as something like an expert but didn't seem to get anything right. I think Prince Charles could possibly be regarded as a thought leader in the Green movement.