Nobody has all the facts. Even text books are frequently rewritten to become more inclusive. Sometimes the simplest request can stump an expert. If the situation is critical or school related or an innocent bet with a friend a fast accurate reply is appreciated. If there is an expertise that is relevant in a certain area it is possible to start making money answering questions.
Perhaps work experience or educational endeavors can expedite a reply. Contacts or past encounters in the same problem area provide a backdrop for similar or related experiences. Get into a position to benefit from knowledge gained through experience or training. Categorize and provide a response in an understandable fashion that does not generate need for follow up.
Determine the amount of available time and set aside a period to accept queries. The determination of amount of expertise will weigh heavily in acceptance in a category. Obviously a passing acquaintance with subject matter does not qualify someone for expert designation. Good intentions are not a valid explanation if someone was misled because the depth of experience or research was not sufficient.
In addition to the normal or quirky kinds of queries there are classifications that can range from legal to medical or sports statistics. The list of possibilities is endless and therefore there is room for those with the desired skill level to participate and benefit financially. The broader the background the more chances to receive a profitable volume of inquiries.
If retired more time could be devoted and a part time effort expanded to a full time occupation. As careers advance and the pressure to advance in business increases questions increase. Expectations that were once limited to what could over a period of time be researched from books have changed. Immediate, accurate and well written documentation have become expectations that cannot be dismissed.