This article aims to identify notable Ethno/mathematical practices in commercial activities among entrepreneurs/sellers in the reference market. We are concerned with knowing how these practices, notable in the informal economy, can influence the teaching of Mathematics in the classroom, based on theories of Ethno/mathematics. To meet the proposed objective and considering the nature of the topic, the research was developed using qualitative methodology, where information was obtained through direct observations and the application of semi-structured interviews to six informal sellers, with greater consistency and details of three sellers. After obtaining information, a reinforced analysis of reports was carried out, investigating knowledge of informal and implicit Mathematics, whose practices lead us to Ethno/mathematical knowledge. Bibliographical research was also used using authors of scientific recognition such as D`Ambrosio (2013), Lúcio (2019), Saraiva (2011), Gerdes (2007) among others. In short, informal sellers use an (Ethno)mathematics that they developed from the transmission of values coming from generation to generation, by the elderly, but which allows them to develop the four fundamental operations of Mathematics (Addition, Subtraction, Multiplication and Division), measures of weight and length. Identifying commercial know-how and considering the mathematics practiced by salespeople and school Mathematics, we developed pedagogical proposals for teaching Mathematics in the classroom, for students in Primary Education and the first cycle of Secondary Education. The suggestions presented will serve as support/reinforcement for researchers and teachers, since the topic under study is open.