Purchasing products from online e-stores is getting popular with the advance of Internet infrastructure and network security. At current stage, most e-stores resemble vending machines rather than real stores because they lack clerks to persuade prospects into buying products and to bargain with the customers for making a good deal. This research aims to design an easy-to-use and autonomous sales-agent, called Isa, to act as a virtual clerk in an e-store. A new approach is proposed to enable the agent to dynamically adopt different persuasion and negotiation strategies according to different characteristics of human buyers. Additionally, this approach enables a sales-agent to learn the best strategies without seller¡¦s instructions. Both laboratory and field experiments are conducted to assess Isa¡¦s performance. The experimental results reveal that Isa can improve a seller¡¦s surplus and increase a buyer¡¦s product evaluation, willingness to pay more money for the product, and satisfaction with visiting the s-store.