In dynamic cooperative architectures that are based on services (SOA), Customers are not only interested in service functionalities, but also in their quality, such as performance, cost, reliability, security and so on. In this scenario, models, techniques and tools supporting the selection of the best service are needed. In this paper, we propose an evaluation framework that includes a flexible quality meta-model for formalising Customer and Provider views of quality, and a decisional model defining a systematic approach for comparing offered and requested quality of services. We also illustrate the applicability of the framework in a Web Service(WS) scenario.