This is by a policeman, written to train rookie policemen in how to extract money "on the side" from their job as a policeman. Some people would call that corruption or bribery. The author takes pains to never take a bribe, but always to receive gifts from thoughtful citizens and business owners due to how he saved them a lot of time, money and trouble by deciding not to arrest or cite them, or by stopping by their business regularly to make sure there's no trouble there.