The aim of this paper is to present the use of a decision function in the implemen-tation of a multi-agent simulation model of a small-sized enterprise dealing with trading. The subject of the presented research are simulation experiments in MAREA software framework, which was designed to simulate trading behaviour of a trading company. Firstly, we present a multi-agent system and a mathemati-cal description of a decision function, which is used to establish the price of trad-ed goods. Secondly, we present MAREA software framework and lastly we dis-cuss the simulation results of company dealing with retailing of fluorescence col-ours. The results obtained show that simulation experiments in MAREA could be used to support the decision-making process of a management of trading compa-nies in the scope of predicting key performance indicators and changes of param-eters and their impact on the company's financial balance.