Digital transformation has amplified the prevalence of manipulative interface designs—commonly known as dark patterns—which influence consumer decision-making and raise critical ethical concerns in online commerce. Although international research has grown, little is known about their psychological and behavioral impact within the Portuguese context. This study addresses this gap through a mixed-methods approach. A qualitative focus group with university students revealed three central themes: recognition of manipulation, emotional reactions such as frustration and loss of control, and appreciation for ethical alternatives, namely mindful commerce. Complementing these insights, a quantitative survey of 162 consumers demonstrated that perceived exposure to dark patterns significantly decreases trust, loyalty, and purchase intention, confirming all proposed hypotheses. Together, the findings extend existing literature by providing context-specific evidence and illustrating the normalization of manipulative design in digital life. From a managerial perspective, the results emphasize the need for transparent, user-centered, and ethical design strategies to build sustainable consumer–brand relationships. Overall, the study underscores that while dark patterns may generate short-term benefits, they ultimately undermine the trust and loyalty on which digital commerce depends.