Format-Store is a serious game application designed for training salesmen and managers in the context of a retail store or a larger supermarket. In this paper, we argue that a relevant way to train a salesperson to their daily activities (e.g. customer relationship manage- ment, store management and stock control) consists in immersing them in a 3d environment populated with realistic virtual customers. The first part of this paper presents the multiagent approach we apply to the de- sign of the intelligent customers. Specifically, we analyse the contribution of the interaction-oriented methodology IODA in facilitating the conception of a game for non computer-scientists by means of a user-friendly design tool and the automated implementation of the conceptual model. The second part describes the organisation of the game around scenarios modelled with respect to the pedagogical requirements. We discuss how the multiagent simulation is wrapped by several modules for the purpose of controlling the learning experience of the player.