The price of a product or service is the decisive criterion for many consumers when making a purchasing decision. Nevertheless, many do not want to forgo the familiar expert advice and on-site service. Julia Weisser investigates which strategies proposed in theory to protect against opportunism can be successfully applied in practice. To do this, the various forms of opportunistic behavior that can occur in consulting services must first be identified and explained. The New Institutional Economics will serve as the theoretical basis for the investigation. With its help, a distinction will be made between the different types of opportunism, and approaches to solving the opportunism problem will be derived.