Exchanges between Internet users have clearly increased with the proliferation of social networks. That has revalorized Consumer-to-Consumer (C2C) Websites which represent an important information source for clients. With the increase of actors in C2C markets, the reputation of the company is a fundamental element for internet users' choices. The objective of this research paper is to identify the factors that can affect the companies' reputation whose products are sold by consumers in C2C websites. A qualitative study was conducted. This study is based on the analysis of ads' content of two Tunisian C2C websites as well as interviews with C2C websites' users. The results highlight the determinants of companies' reputation in C2C websites: quality of the classified advertisements, quality of the C2C website, price and electronic word-of-mouth (as a receiver). All these elements affect companies' reputation in C2C website users' mind. This reputation can also have consequences, such as electronic word-of-mouth (as a sender) and intention to buy the companies' products in the future.