Online shopping sales have experienced rapid growth in recent years, with the COVID-19 pandemic further accelerating the global adoption of e-commerce (EC). For EC platforms, understanding the factors influencing consumers’ shopping decisions is crucial. Previous studies have explored decision-making behaviors through factors such as online reviews, product recommendations, and promotions. These elements, which are part of the user interface (UI) of websites, significantly influence the user experience (UX) of consumers. However, the impact of UI elements on UX during online purchasing decisions has not been fully explored. Moreover, dark patterns have become significant focus in UI design due to their tendency to drive undesirable consumer decisions. For apparel EC, it is crucial to offer a superior UX during the purchasing process compared to other platforms. This study explores the effect of UI elements with dark patterns on purchase decision-making in apparel EC. While various UI elements can be found on apparel EC sites, this research focuses on three shopping stages: product descriptions, recommendations, and online reviews, analyzing two apparel EC sites. The UX curve method and protocol analysis are used to investigate the relationship between purchasing behavior and the shopping experience. We examine UI elements such as photos, textural descriptions, and product attributes before making a purchase decision based on these elements. We propose a multi-stage UX curve method to analyze how UX evolves over time and affects purchasing decisions. The findings demonstrate the dynamic influence of UI elements with dark patterns on consumer UX, offering valuable insights for improving the design of EC platforms.