Sales and negotiation are important, not only in business, but also in private life. This final thesis is primarily about principled sales, about salesperson characteristics, communication, negotiation and negotiation techniques, but also about sales effectiveness. Selling requires direct communication with the customer, and the seller should master a number of different skills and knowledge. The paper begins with a theoretical part that served as a framework for research, and is based on literature relevant to the topic of the work. A variety of different textbooks and books related to this area were used, as well as a number of scientific articles that previously dealt with this issue. The theoretical framework that covers all essential elements is followed by the empirical part of the paper. The following hypotheses were set for the research: H1 – Sales personnel whose organizations achieve a higher level of efficiency apply sales skills adapted to the customer's profile; H2 – Knowledge of sales techniques and negotiation skills affects the sales and post-sales results of the organization; H3 – The individual performance of seller aimed at achieving sales results is significantly better in well-organized and efficiency-oriented organizations than in those where the situation is different. For the complete analysis, 228 respondents were included. The mentioned hypotheses were fully confirmed. Negotiation skills include the seller's actions taken before contact with the customer, preparation and planning of negotiations, and after contact, analysis and evaluation of the results. Sales and negotiation skills require continuous practice, learning and improvement in order to achieve good sales results. In addition, in organizations that nurture internal communication with employees and invest in their knowledge by conducting training, they increase employee motivation and consequently increase sales results.