The alignment of the context information with the service objectives facilitates the successful provisioning of context-aware services. Moreover, the fact that context may come from transient and/or unreliable sources needs consideration. False or stale context can dramatically affect the decisions and the actions taken by context-aware services. This paper presents an approach for evaluating and selecting the information to be used by context-aware services that takes into account the quality of information, and automatically adapts to any source changes and failures. The proposed quality-aware discovery of context information sources allows services to be ported easily to environments with different sets of sources.