In a service-oriented e-commerce environment, it is a crucial task to help consumers choose desired products efficiently from a huge amount of dynamically configured product candidates. Decision agents can be designed to provide interactive decision aids for end-users by eliciting their preferences and then recommending matching products. In reality the users' preferences may keep changing along with the dynamic decision environment and may not be fully satisfied. As a result, the decision agent is required to be agile; it should allow decision making with an incomplete user's preference model and should afford users to add, retract or revise their various preferences with little effort. In this paper we propose the general design of an agile decision agent to meet this need. We model users' preferences with the soft constraint technique and elicit them by the example critiquing interaction paradigm