Retnawati, Berta Bekti, and Nuryakin Nuryakin. 2016. “Developing Salesperson Performance: The Role of Customer Encountering Competence Portfolio, Relational Capital and Service Excellent Customer Heterogeneity”. International Review of Management and Marketing 6 (4):891-97. https://econjournals.net.tr/index.php/irmm/article/view/3093.