Is appellant's role in the crime reduced to a reduced level of responsibility for the crime?

Finally, appellant challenges the district court's two-level upward adjustment for his role in the offense. This adjustment was based on the testimony of two co-defendants who stated they worked for the appellant and were being paid by him. Appellant on appeal challenges their credibility, but there is no basis in the record to substitute our judgment for the decision of the district court on that issue. Therefore, the district court's characterization of appellant as a "supervisor" was not clearly erroneous. Cf. United States v. Peters, 962 F.2d 1410, 1415 (9th Cir.1992).