In order to support business service flexible and reusable, it is desirable to provide users or applications the same service but with different service quality, different interaction paths, or different outcomes. We call this design principle as Service Differentiation. In this paper we present a fully working service design method where variability is externalized as business policies so that the business $process(es)$ does not need to be altered for any anticipated changes. Service differentiation is realized by configured business processes and interfaces, and the dynamic 'binding' between user/application with a specific interface is determined by policy during service invocation time.