## 6 Conclusions  
This study aimed to propose usability evaluation indicators and their weights for second-hand trading applications, enhance user stickiness, and reduce app uninstall rates. Through a literature review, 29 usability indicators were summarized. Using the Delphi method with 20 experts, these 29 indicators were refined by removing duplicates and merging similar ones, resulting in 23 usability indicators: Satisfaction (C1), Flexibility (C2), Accessibility (C3), Social (C4), Pleasure (C5), Value Realization (C6), Efficiency (C7), Memorability (C8), Convenience (C9), Simplicity in Use (C10), Learnability (C11), Error Prevention (C12), Immediate Feedback (C13), Interface Simplicity (C14), Help (C15), Consistency (C16), Error Feedback (C17), Findability (C18), Page Information Architecture (C19), Navigation (C20), System Security (C21), Property Protection (C22), and Privacy Protection (C23) (addressing RQ1). Next, these 23 indicators were grouped and named through Exploratory Factor Analysis (EFA). The indicators were classified into five groups: Emotional Design (B1), Learning and Operation (B2), Interaction Experience (B3), Information Architecture (B4), and Security and Privacy (B5). Finally, the Analytic Hierarchy Process (AHP) was used for hierarchical  
Figure 9: Composite weights. structuring. The primary indicator Emotional Design (B1) includes the following secondary indicators: Satisfaction (C1), Flexibility (C2), Accessibility (C3), Social (C4), Pleasure (C5), and Value Realization (C6). The primary indicator Learning and Operation (B2) includes Efficiency (C7), Memorability (C8), Convenience (C9), Simplicity in Use (C10), Learnability (C11), and Error Prevention (C12). The primary indicator Interaction Experience (B3) includes Immediate Feedback (C13), Interface Simplicity (C14), Help (C15), Consistency (C16), and Error Feedback (C17). The primary indicator Information Architecture (B4) includes Findability (C18), Page Information Architecture (C19), and Navigation (C20). The primary indicator Security and Privacy (B5) includes System Security (C21), Property Protection (C22), and Privacy Protection (C23) (addressing RQ2). Lastly, based on the expert ratings, the weights for different levels of indicators were obtained, including their overall weights. Among the primary indicators, the highest weight was for Security and Privacy (B5, 0.4094). Within the Emotional Design (B1) indicator, the highest-weighted secondary indicator was Social (C4, 0.3336). Within the Learning and Operation (B2) indicator, the highest-weighted secondary indicator was Simplicity in Use (C10, 0.3464). Within the Interaction Experience (B3) indicator, the highest-weighted secondary indicator was Consistency (C16, 0.4661). Within the Information Architecture (B4) indicator, the highest-weighted secondary indicator was Page Information Architecture (C19, 0.5813). Within the Security and Privacy (B5) indicator, the highest-weighted secondary indicator was Property Protection (C22, 0.5485), (addressing RQ3). The findings of this study can serve as a comprehensive guide for enhancing the usability of second-hand trading apps through design, which is crucial for assessing and improving app usability. By enhancing the usability of these apps, we can increase user engagement, encourage the purchase of second-hand products, and reduce waste generation, thereby positively impacting environmental conservation. However, a limitation of this study is the small number of experts involved in the surveys, which did not allow for a sufficiently diverse range of opinions. Additionally, the selection of usability assessment indicators for mobile second-hand trading apps was solely based on a literature review. In consideration of these factors, future research plans should aim to expand the pool of experts participating in the surveys and the range of selected indicators toward more systematically gathering and integrating a broader spectrum of opinions and indicators. Conceptualization, X.L. ; methodology, X.L. ; software, X.L.