Background: Seller opportunism is quite prevalent online and raises the overall cost of the transaction. Online transaction platforms are more vulnerable to seller opportunism than traditional businesses. The few studies on online opportunism are quite fragmented. This study synthesizes the existing literature and presents an integrated framework for understanding seller opportunism on online platforms.

Method: We use a structured literature review approach following Schryen’s guidelines and Webster and Watson’s suggestions to identify relevant articles on opportunism from the Web of Science and Scopus databases published between 2003 and 2023. We derive additional articles from Google Scholar and AISeL and finally have 61 articles. We use a thematic analysis approach to analyze the articles.

Results: We synthesize the findings into a comprehensive seller-opportunism framework that elucidates the three essential themes of seller opportunism: the rationale and favorable conditions for opportunistic behaviors, the impact of opportunism, and measures to counter opportunism. The study identifies transaction-specific investments, behavioral uncertainty (platform uncertainty, seller pseudonymity, and product uncertainty), and environmental uncertainty (high competitiveness, nature of e-commerce transactions) as causes of seller opportunism. Platforms can counter such opportunism by building pre-purchase trust (such as improving product informativeness, building online communities, integrating escrow accounts, implementing sellers’ reputation system, improving contract design, and enabling AI-based tools to identify copied images) and implementing post-purchase regulations (formal and informal agreements).

Conclusion: The comprehensive literature presents a holistic understanding of seller opportunism on online platforms. The seller-opportunism framework enhances the transaction cost economics theory online, especially identifying transaction-specific assets and uncertainty as significant causes of seller opportunism. The framework will be helpful for online transaction platforms for better governance. It will also be useful for regulators to develop better regulatory policies governing online transaction platforms.