## 4 Research Execution and Analysis  
### Extraction of Usability Indicators  
In Usability Engineering, Nielsen defines usability as the measurement of whether a system or product meets consumer requirements, categorizing it into five aspects: Learnability, Efficiency, Memorability, Errors, and Satisfaction [58]. The ISO 9241 standard [59] defines usability as the extent to which specified users can achieve specified goals with Effectiveness, Efficiency, and Satisfaction in a particular context of use [60]. [PERSON]'s definition emphasizes the necessity of system evaluation throughout the development life-cycle, highlighting four criteria of a usability system: effectiveness, learnability, flexibility, and user attitude [61]. [PERSON] and [PERSON] (1994) described usability in terms of enhancing the speed and ease for users interacting with a product to achieve their objectives. Usability can be encapsulated as emphasizing user centricity, effectiveness, efficiency, and ease of use alongside the aspects of effectiveness, efficiency, and simplicity in use [62]. The above is based on the literature and compilation of usability indicators. However, considering the specific research subjects, further literature research on the usability of applications is needed. So, we considered the variability in usability across different researchers or fields not only by referencing the indicators of usability evaluation provided by scholars but also through utilizing widely recognized platforms such as Scopus, Web of Science, and Google Scholar [63, 64]. Keywords including \"app usability research\", \"interface design\", and \"online second-hand trading app\" were used to search the literature. The aim was to comprehensively select usability indicators for second-hand trading apps from multiple perspectives. [PERSON] (2023) classifies the usability of app software interfaces into several categories: timely feedback on software operations, terminology understandable by users, clarity of the interface, consistency with public cognition, realization of value through application use, error feedback that notifies users of operational mistakes, assistance that offers solutions, privacy protection safeguarding user privacy, and protection of property [65]. In their study on the factors influencing satisfaction with app interface \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{N=20}\) & **Item** &
\begin{tabular}{c} **Number of** \\ **Participants** \\ \end{tabular} & **Percentage (\%)** \\ \hline \multirow{2}{*}{Gender} & M & 7 & 30 \\ \cline{2-4}  & F & 13 & 65 \\ \hline \multirow{3}{*}{Occupation} & Product Managers & 3 & 15 \\ \cline{2-4}  & Interaction Designers & 7 & 30 \\ \cline{2-4}  & Product Designers & 10 & 50 \\ \hline \multirow{3}{*}{Education Level} & Bachelor’s Degree & 3 & 15 \\ \cline{2-4}  & Master’s Degree & 5 & 25 \\ \cline{2-4}  & Ph.D. & 12 & 60 \\ \hline \multirow{3}{*}{Work Experience (years)} & 10–14 & 8 & 40 \\ \cline{2-4}  & 15–20 & 10 & 55 \\ \cline{1-1} \cline{2-4}  & Over 20 years & 2 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._design, [PERSON], [PERSON], and [PERSON] (2021) detailed that interface clarity, simplicity, and the layout of graphics and text significantly impact the usability of app interfaces [66]. [PERSON], [PERSON], and [PERSON] (2021) described the usability of mobile applications through seven indicators in their article: \"usable\", \"usefulness\", \"desirable\", \"findability\", \"accessibility\", \"credibility\", and \"valuable\" [67]. [PERSON], [PERSON], and [PERSON] (2019) demonstrated in their study that when using second-hand trading software, the software convenience, the pleasure derived from purchasing products, the social aspect of communicating with sellers, and the security of the payment system are aspects that capture consumer attention [68].