In this paper, we address the problem of provisioning unreliable and heterogeneous service providers for the constituent tasks of abstract workflows. Specifically, we deal with unreliable providers by provisioning multiple service providers redundantly for specific tasks, and we employ a local search mechanism to choose among many heterogeneous providers that offer the same type of service. We empirically show that our strategy can achieve significant improvements over current approaches, and we demonstrate that it works well over a range of environments.