Purpose - The purpose of this paper is to investigate the influence of informal Korean social networks ( Yongo) on sales activities in Korea, by focussing in particular on required vertical core competencies. Design/methodology/approach - The authors draw on expert interview data gathered in Korea in two waves ( 2009 and 2012). Whereas first-wave interviews served to identify the influence of Yongo on sales management in general, second-wave interviews data - gathered from a Korean auto maker, a Korean supplier, and an international supplier - served to derive vertical core competencies vital for sales executives in Korea. Findings - The authors find Yongo to be an indispensable aspect of relationship management in Korea. Further, the authors propose ten vertical core competencies and skills sales managers in Korea need to possess, e.g., respecting strong hierarchical supplier-customer relations, the ability to engage in relational contracts, establish trustful relationships, and perform in a risk-taking manner in a dynamic environment. Originality/value - So far neither Yongo nor its impact on successful sales management in Korea has been analyzed. Hence, this research provides initial insights into the modes of action of Yongo in sales management, which is of particular importance for management consultants and international sales managers and executives.