Indonesia's e-commerce sector is booming due to increased internet use, making seller satisfaction and loyalty vital for platform success. This study explores how service quality shapes these critical aspects, aiming to build a comprehensive model. We employed Partial Least Square Structural Equation Modeling (PLS-SEM) and Importance-Performance Map Analysis (IPMA), utilizing the e-MerQual framework's four dimensions: reliability and privacy, efficiency, value-added service, and information usefulness. Data were gathered from active sellers on Indonesia's Shopee platform. Our findings indicate that while all service quality dimensions significantly enhance seller satisfaction, their impact on loyalty is fully mediated by satisfaction itself. Higher satisfaction leads to greater loyalty and a reduction in complaints, while complaints, in turn, negatively affect loyalty. Importantly, IPMA highlighted reliability and privacy, particularly the speed of issue resolution (RP7), as the top priority for service improvements. This research offers both theoretical insights into e-marketplace seller dynamics and practical guidance for strategic seller management and competitive advantage. © 2025 KIIE