As services are developed by independent providers, it is impossible to predict all potential interactive possibility at development stage. In order to ensure the correct service collaboration, it is necessary to check the interaction compatibilities among participating services. This paper presents a top-down approach to improve the reusability of available services and the flexibility of service collaboration based on a decentralized mediation model. Through failure-equivalent projection, the collaboration process is transformed to decentralized processes, which facilitates a more efficient pair-wise compatibility check. A mediation-based method is proposed to check if the compatibilities can be achieved by using mediation mechanism. Algorithms of compatibility check and automatic mediator generation are also provided. This approach makes the coupling between available services and collaborative environment more looser, thus improving the flexibility of collaboration while preserving the autonomy of services.