Your plumber's personal agenda aligns with yours: you want the pipe repaired and you don't even mind to pay X, the plumber wants to receive X and he doesn't eve

Your plumber's personal agenda aligns with yours: you want the pipe repaired and you don't even mind to pay X, the plumber wants to receive X and he doesn't even mind to repair your pipe. His knowledge is used in your interest also. Politicians, by the other hand, may know more than us but that knowledge may or may not be used in our interest.