Sherlock Holmes has an excellent income and an interesting life as a "consulting detective." He actually leads an enviable life of leisure. He has the reputation of being a great genius in his special field. When he says that frankness would spoil his reputation, he only means that if he made a habit of explaining his methods of deduction many people would stop believing that he was something of a wizard with magical powers. He occasionally explains some of his conclusions to his friend Dr. Watson, and invariably Watson ceases to marvel when he realizes that the conclusions were based on simple observations and obvious deductions.
Holmes is especially observant, and many of his deductions are derived from what anybody could plainly see if they took the trouble to look. Holmes is motivated to preserve his good reputation because it brings him clients, the clients pay him money (most of the time), and the money enables him to lead his enviable life of leisure. The typical reader of the Sherlock Holmes stories in Victorian times was a lazy middleaged man loafing in an easy chair, smoking a pipe, and sipping a little sherry. He was reading about a man who could earn a good living while spending most of his time loafing, smoking a pipe, and sipping sherry in a comfortable sitting room.