Abstract: The subject of the present invention is a method for certifying an opinion relating to a product or service written by an author, user of a terminal, on a server managing a space dedicated to the expression of opinions, the terminal and the server being integrated into a network, characterized in that the method involves a certification system and comprises: a step for transmission by a communications interface of the system of a request, destined for the identifiable author, for a proof authenticating the purchase or the use of the product or service by the author, a step for communication of an element for authentication of a purchase or use by the identified author, a step for analysis of the authentication element by a unit of the system associated with a database, a step for generation of a certificate, a step for transmission of the certificate to the server managing the space for expression of opinions, a step for association of the certificate with the opinion written by the author.