The aim of this research was to provide a better understanding of factors influencing the performance of (small) agricultural producers. Considering the importance of agricultural producers, not just for maintaining a steady supply of products but also for the preservation of the population (and cultural tradition) of rural areas, the development of sustainable agricultural business is a matter of public interest. This paper considers wine producers and their market channels, i.e., the factors influencing the relationship between wine producers and market intermediaries, by applying ideas taken from agency theory. We developed a conceptual model with our defined measure of agency costs as the mediator variable between multiple regressors and the firms’ financial and non-financial performance as regressions. We used the approach of Baron and Kenny to investigate whether agency costs act as a mediator variable. The data needed to test the proposed conceptual model were collected through questionnaires and contextual interviews with the Croatian wine producers (n = 124). We found that more self-reliance in the distribution process, supported by factors related to the bargaining strength, had a positive influence on wine producers’ performance. The results also support the assumption that agency costs act as a full mediator variable between a producer’s attributes and its performance.