In this paper we analyze how the way in which the principal's preferences are visualized may affect the accuracy of representation of this principal by their agent. We study the processes of multi-issue electronic representative negotiations conducted by agents on behalf of their principals by means of the negotiation support system that implements a simple decision support tool for eliciting the preferences and building a system of cardinal ratings for feasible negotiation offers. First, we investigate the accuracy of agents' scoring systems and compare their concordance to the preferential information provided to them by their principals by means of single verbal description and two different visualization techniques, one using bar graphs and the second-circles (pies). The concordance is measured by means of the notions of ordinal and cardinal accuracy. Then we analyze how the scoring systems with various inaccuracy indexes influence the agents' perception of negotiation process, i.e. the interpretation of concessions made by parties and the structures of concession paths. We also study what is an impact of inaccurate scoring systems on the negotiation outcomes, i.e. the final contracts, their ratings and efficiency. The results obtained show that the bars are slightly better in more precise representation of principals preferences. They allow agent to determine a little more accurate scoring systems, which help to understand the negotiation process better by minimizing the cardinal error of evaluation of the offers in concession paths. Yet, no significant impact on the outcomes have been found. An interesting prescriptive conclusion that can be drawn is that to assure an adequate representation of principal's preferences the agents should be offered the bar-based visualization. Also, a checkup mechanism should be introduced to the preference elicitation procedure that assure the agents to be ordinally concordant with the priorities of their principal's preferences.