This study confirmed the relationship between variables developed by qualitative ground theory through quantitative research. The purpose of the study is to explain the effect of core sales tasks on sales services and the mediating effect of organizational member relationships on sales services. The data were collected through a survey of fashion brand salespeople in Gwangju from September to October 2020 with data from 235 responses analyzed using SPSS 27.0 and AMOS 26.0. The validity of the research model verified the confirmatory factor analysis and the research hypothesis was verified through path analysis and multi-mediated analysis of the structural model. The research results were as follows. First, sales management did not directly affect sales services, and customer management affected sales services. Second, a meaningful causal relationship was shown to exist between organizational member relationships and sales management, but organizational member relationships and customer management did not have a significant relationship. Third, the total and individual indirect effects of headquarters relations, colleague relations, and customer management were all statistically significant.