As part of a larger research project to understand and improve motivation in an XP-based, software development organization, we undertook a study to investigate the impact of customerdeveloper interactions on motivation in this organization. Among the impacts found, an individual's perceived level of control within the interaction emerged as significant. We describe the specific behaviors which shape an individual's perceived control, and thus motivation, in our context, and investigate the underlying causes for these behaviors by assessing them in accordance with extant social-psychological theory. We find that the very nature of XP itself imparts strong psychological pressures on participants which can positively affect their interactions, and thus, motivation. However, these pressures also contribute to de-motivation in our context, when their effects on customer-developer interactions are not appropriately monitored and mitigated.