The Suck Up Project (2012) on Netflix

Plot summary

At a large insurance company, Dong-sik is the employee who does everything by the book while his colleagues chase promotions through schmoozing. His strict ethics cause him trouble at work and at home, and he is demoted to insurance salesman, where his tactlessness and lack of charm hold him back. He learns that his mother borrowed from a loan shark to fund his father's promotion to principal of a local school. To lift his sales and repay the debt, he approaches Hyeo Go-soo, a legendary master of flattery whose book on wooing and persuading others is prized by salesmen. Hyeo Go-soo agrees to teach him, and Dong-sik sets out to follow the lessons.