The district court erred in requiring an employer to prove by clear and convincing evidence that an employee fell within the outside salesman exemption from the FLSA’s minimum wage requirements. The statute is silent as to the standard of proof for exemptions. So the ordinary civil standard of proof by a preponderance of the evidence applies. More stringent standards of proof are required in civil cases only where required by statute or constitutional provisions or where the government is taking particularly coercive action, such as taking away a person’s US citizenship.