This study examines user reactions to in-app advertising within self-scanning systems in retail, with a focus on how different advertising formats impact user experience. Through a mixed methods approach, a prototype application simulating a self-scanning interface was developed, featuring five advertising variants ranging from non-intrusive banners to highly disruptive full screen ads with forced exposure. Data were collected from 40 participants via structured surveys and open-ended responses.The results indicate that advertising intrusiveness significantly influences user irritation, perceived control and behavioral intentions such as app avoidance. Non-intrusive formats, such as static banners, were well tolerated and perceived as acceptable, whereas forced and visually aggressive ads led to strong negative emotional responses and reduced user engagement. Key moderating factors include perceived relevance, user control and ad tolerability, which can mitigate negative reactions when appropriately integrated.The study offers practical design recommendations for implementing advertising in self scanning systems, emphasizing subtle integration, user autonomy, contextual relevance and avoidance of disruptive formats. These findings contribute to both academic literature on digital advertising in task-oriented environments and practical guidelines for retailers seeking to balance monetization with user experience.