Knowledge sharing among partners from a distributed engineering team is becoming more critical for decision making. The work presented in this article proposes to support users of an agent based application for collaborative product design, during the definition of an engineering problem under a Constraint Satisfaction Problem (CSP) approach. The scope of this work covers the domains definition for variables from the CSP distributed model. A semiautomatic negotiation model is proposed in order to give users suggestions about a preferred domain for a variable that is used for more than one expert. A set of quantitative indexes measure the competence that users have over variables in the model, helping the system in decision making. A fuzzy inference system is used to calculate user’s competence index and suggestions are made based on a fuzzy approach in order to achieve trade-offs in collaborative domains definition.