Exchanges between service providers and their customers on business markets increasingly take place in the form of long-term business relationships. These relationships are governed through formal or informal agreements. However, actors are bounded in their rationality and find it impossible to contemplate all possible future contingencies. The more formal and detailed the contracts they conclude, the likelier it becomes that at least one actor is going to perceive a need to adjust the initial agreement as environmental events unfold. In this case, the actor relies upon his partner's flexibility. This paper deals with service providers' flexibility and presents empirical results from the market research sector including outcome variables (satisfaction, trust, commitment) and determinants of service provider flexibility (uncertainty, relationship-specific investments, mutuality, long-term orientation). Empirical results suggest that service provider flexibility is an important determinant of customer satisfaction, trust, and commitment.