We present a model of negotiation dynamics whose aim is that of mimicking the mechanisms leading to opinion and convention formation in a population of individuals. The key elements of negotiation are memory and feedback, while processes of opinion formation are usually modeled exploiting local majority of imitation rules. The model displays a non-equilibrium phase transition from an adsorbing state in which all agents reach a consensus to an active not-frozen stationary state characterized either by polarization or fragmentation in clusters of agents with different opinions. The transition is driven by external noise, intended as an irresolute attitude of the agents in making decisions. As a notable example we discuss the application of this modeling scheme in linguistics.