Deciding on "expert" seems completely intractable. What if one fellow has spent a decade studying the subject and agrees with 90% of his fellow decade-studiers on 90% of things but the remaining 10% of topics he has views shared by approximately no one. Is he a crank or an expert? What if he's fairly persuasive to layman/politicians and thus is the head of the Bank of England?

Additionally, if a subject matter does not lend itself to experimentation or feedback mechanisms then you can easily have all the experts be consistently wrong for decades due to group think or conformal pressures.