To judge from the movies and from best-selling crime novels, a private investigator is short on ethics and long on knowledge of how to get the juicy facts on people. They do this by using thoroughly illegal methods, while just barely managing to avoid getting arrested. The truth, of course, is that most PIs run entirely legitimate businesses. Since many of them started their working lives as sworn law enforcement officers, they know perfectly well what's legal and what isn't, and most are not tempted to cross the line.