The Doctrine of Exchange is a central tenet of Scientology, which dictates that for spiritual well-being, "anytime a person receives something, he must pay something back" and balance "inflow" with "outflow". The Church of Scientology has presented this as the reason why some of its services, such as auditing (a central practice, and sometimes described as the central practice of Scientology), must never be given away, to members who are at the church, but must be paid for. This is frequently used by the Church as an explanation for the fixed pricing of its many fees.