The study reported in this article is based on theories about job and competence analysis and a project in which job profiles were developed that were aimed at providing a framework of reference for evaluating in-service training programmes for purchasing professionals (professional buyers of goods and services in various sectors of the economy) provided by a training institution of an association for purchasing management. This project was commissioned as part of the permanent maintenance policy of the training institution, but also based on experience with an earlier comparable project, and concerns about test development using job profiles and related attainment targets. The study is part of a research programme on course development for professional training. Ideas about course content validation were explored and tested. The article addresses the issue of trustworthiness and uncertainty reduction in the job profile research process. It specifically looks at the methods used in job profile development and perennial research problems that are related to that, such as stratification of a professional sector, sector-specificity of job information, formatting job profiles, and the value added of small-scale in-depth analyses of work processes versus large-scale job surveys. It concludes that small-scale, context-related analyses of jobs adds most value, but that this is not sufficient for ensuring faith in the study results. Large-scale surveys complement the in-depth analyses in this respect. So using a mix of in-depth and large-scale methods is recommended in conducting job profile research.