The current Internet based electronic market has limited capability in customizing the customer``s needs. It merely displayes the picture and description about the products. To overcome such a limitation, we attempt to design and develop an Cyber-salesman expert system. To fulfill this end, we need to achieve the following goals. 1) salesman``s strategy 2) Develop an interactive reasoning procedure so that a customer can find a satisfactory solution with a flexible tradeoffs,but within a shortest time. 3) Develop an architecture that can implement the idea on the Internet 4) Demonstrate the validity of the approach and system with a real world example 5) Develop a knowledge acquisition and maintenance method for multiple number of products Those goals are achieved by adopting the Constraint and Rule Satisfaction Problem (CRSP) for the represention with the concurrent reasoning technology which allows the interactive tradeoffs between the product``s functionality and price.This framework is implemented the using Java to run on the Internet. We could confirm that this prototype system named Cyber-SES performs very well. Cyber-SES is demonstrated with the purchase support of audio and video equipments and men``s wear. To apply Cyber-SES to multiple products, we have proposed a template-based approach. By developing several typical knowledge templates, the CRSP model can be automatically generated by simply inputting the knowldge of each case. We have tested the validity of this approach with 10 products, and confirmed its effectiveness. Cyber-SES must contribute to the customized purchase of cyber-shopping.