There is a widely believed tradition that good or high-quality agency–client relationships make for superior advertising campaigns, with many scholars highlighting the benefits agency professionals bring to the advertising creative development process. However, not all agree, and some scholars point to a “dark side” of apparently good relationships—an alternative tradition that is based on agency theory. This approach suggests agencies can take advantage of clients who are highly committed. Our research focuses on the agency perspective to this question and collects data on 518 campaigns from London and Amsterdam agencies. We show both traditions have merit in that the two processes operate simultaneously. When agencies perceive that the quality of their client relationship is low, the professionalism of agency personnel shines through developing original, strategic, and creative work. But when relationship quality is considered high, dark side problems emerge. However, there is a bright side to good relationships. Creativity theory suggests that a good relationship can increase the intrinsic motivation of agency staff such that their increased passion for the work offsets dark side problems—something for which we find empirical support.