McDonald, M. How to sell a service, 1986: t.p. (John Leppard) p. 4 of cover (consultant specializing in management development, marketing, and designing training packages; visiting lecturer at Cranfield Sch. of Management)

McDonald, M. The marketing audit, 1991: t.p. (John W. Leppard)

Auditing your customer service, 1994: CIP t.p. (John Leppard) data sheet (Leppard, John William, b. 11-02-37)

Biblioteca del congreso (Estados Unidos), 20 febrero de 2018: catálogo electrónico https://goo.gl/BbN6Ur