The expansion of online transactions and the rapid growth of trading platforms such as Amazon and Digikala have led to the emergence of legal challenges in the field of civil liability. This study aims to examine the principles of liability of online trading platform owners and to propose innovative approaches in this regard, framing the problem as the incompatibility of traditional civil liability frameworks with the dynamic conditions of cyberspace. The necessity of this research arises, on the one hand, from the increase in electronic interactions, and on the other, from the need to enhance consumer protection in digital environments; as the absence of clear standards for determining the liability of online platforms can result in both financial and non-financial harm to users and diminish trust in online commerce systems. The research methodology is of a comparative-descriptive nature; through the examination of legal sources, regulations, and judicial precedents in Iranian law and European Union law, the differences and commonalities in determining the civil liability of online trading platforms are analyzed, and recommendations are made to improve the liability framework. The findings indicate that despite the existence of general principles of civil liability in both Iranian law and EU law, the adoption of innovative approaches such as the theory of contributory infringement and the doctrine of legitimate expectations, as complementary tools for determining the liability of online trading platform owners, can serve as effective means to protect consumer rights and foster the development of electronic marketplaces.