Most of us do detective work all the time without being conscious of it.

Simply because the matter concerns the theft of a pearl, or the betraying of a business or professional secret, or the disappearance of a friend, the opinion of a stranger becomes no more valuable.

And the chances are equal that the stranger will make a bungle of it.
Many of the best available detectives are men who work by themselves without any permanent staff, and who have their own regular clients, generally law firms and corporations.

Almost any attorney knows several such, and the chief advantage of employing one of them lies in the fact that you can learn just what their abilities are by personal experience.
They usually command a high rate of remuneration, but deductive ability and resourcefulness are so rare that they are at a premium and can only be secured by paying it.

These men are able, if necessary, to assume the character of a doctor, traveller, man-about-town, or business agent without wearing in their lapels a sign that they are detectives, and they will reason ahead of the other fellow and can sometimes calculate pretty closely what he will do.