The Follow (movie, 2001)

The Driver is hired by a nervous movie manager to spy on a paranoid actor's wife. During his tailing of the wife, the Driver describes the right way to tail someone. As he follows her he begins to fear what he might learn of her apparently tragic life. He discovers the wife is fleeing the country and returning to her mother's, and that she's been given a black eye, likely by her husband. He returns the money for the job, refusing to tell where the wife is, and drives off telling the manager never to call him again.