One of the factors that contributes to e-commerce's success, especially in developing countries, is trust. Trust plays a significant role for e-commerce players. To build trust, we need to develop a good reputation. Hence, this research is conducted to examine (identify and prioritize) factors that can develop sellers' reputation in the online market so that sellers would be able to compete and sustain in a competitive market. This research used qualitative and quantitative approach. Seven experts were interviewed in the qualitative approach which validated and thus produced 17 factors. These factors were later categorized using the Value Chain framework. After categorizing the factors, questionnaires were created based on the Fuzzy-AHP framework and distributed to 11 sellers in the top 3 Indonesian e-marketplaces. The analysis of the questionnaires showed that the 3 highest factors that can improve sellers' reputation in Indonesia e-marketplaces are customer services, after sales services, and quality of products.