Service selection and binding for building composite services is a critical but difficult to resolve issue in the domain of service-oriented computing. This paper proposes an innovative approach to address this issue, in which every abstract component service in the composition is assigned a weight value to represent its importance according to designer scoring and basis path analysis, thereby generating a weighted service flow. Composite services, including the selected concrete component services, are produced according to the weighted service flow and genetic algorithms. The generated composite service ensures acceptable quality level and guarantees that the core component services, which are most likely to influence the overall service flow, are more robust than the others. Besides, a novel fault handling method based on the identified core services is proposed to enhance the availability of composite services. Experimental results demonstrate that the proposed approach can effectively maintain the quality of core component services.