The purpose of this study is to understand how social networks affect sales interaction. A small vendor with only one percent delivery share became a single provider of a management service for laboratory equipment. According to formal network theory, this success was regarded as the “fruits” of the vender’s broker position bridging structural holes. Considering the practical needs of salespersons, however, this explanation proves insufficient. As a boundary spanner, they need to know how to gain an advantageous position in their networks. We’d like to explore how they can earn such an advantageous position within their networks. As we’ll subsequently explain later, once the network has changed, it leads to change in relationships between two parties. Changes in cognition could be the key to bring these changes. But they didn’t realize what would be the results of their actions. It could be said that some kind of tacit knowledge is another key. (Coauthor Kenneth Ichiro Tsuye)