Smart proxies are objects often used to adapt and customize distributed object-oriented systems in a non-invasive way. For example, smart proxies are common used to provide support to quality of service attributes. In this paper, we investigate the use of smart proxies in order to provide replication transparency in middleware systems that support the implementation of Web services. The system presented in the paper, called SmartWS, supports the prime replicated server selection policies proposed in the literature. The paper also provides guidelines that help Web service users to choose the policy more suitable to a given application. A new server selection policy that combines several advantages of the already proposed policies is also described. The paper also presents results obtained from experiments performed with a prototype implementation of SmartWS. Such results reinforce the policy selection guidelines presented in the paper.