DiJulius, J. R. (2003). Secret service: Hidden systems that deliver unforgettable customer service. AMACOM.
Lua i Stíl Chicago (17ú heag.)DiJulius, John R. Secret Service: Hidden Systems That Deliver Unforgettable Customer Service. New York: AMACOM, 2003.
Lua MLA (9ú heag.)DiJulius, John R. Secret Service: Hidden Systems That Deliver Unforgettable Customer Service. AMACOM, 2003.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.