What is having to do with the exchange of goods and services

You are the on-duty desk sergeant at the local police station. a man walks in and says, "i killed someone and want to confess." you grab your digital voice recorder and direct the man to a chair. he sits down and tells the tale of what turns out to be a first-degree murder. you record every word, including the numerous instances in which you said, "uh- huh" and "i see." satisfied that the subject did, indeed, commit a murder, you place him under arrest. the confession is: