How and why does Professor Fenton J. Fleabottom deceive people in the novel, The Mostly True Adventures of Homer P. Figg?

Professor Fenton J. Fleabottom poses as a medicine man, who runs a traveling show. He travels around the country, putting on something like a freak show and selling his elixir, a medicine that Homer soon learns is only whiskey. Fleabottom, as we later learn, is actually Reginald Robertson Crockett, a Confederate loyalist who moves around the North collecting information that he then sends to the Confederate military.