The role of sellers is changing in a turbulent business environment and only the sellers who provide first class services and approach to them in a responsible way can survive among competitors. Customers perceive it as an added value and have a good feeling from buying. It is just sellers who are becoming the main factor that contributes to the competitiveness of a whole organization. The segmentation of customers into individual generations enables to better understand their preferences and requirements, it is then possible to predict their tendencies in buying behaviour and thus increasing the sales success. The main aim of the paper is to present the issue of different assessment of sellers' behaviour by the customers of Baby Boom X, Y, and Z generations. In connection with these differences, the aim of the research is to identify generational differences in the assessment of manipulative, assertive, stressed and engaged behaviour of sellers, as well as to analyse the determinants that affect buying behaviour of customers. The research was conducted using a questionnaire method and mathematical-statistical methods on the sample of 207 respondents. The research results confirm the existence of statistically significant differences in assessing the determinants of sellers' behaviour from the perspective of individual customer generations. JEL Classification Numbers: M21, M31, -Z questionnaire (1994), it focuses on the following questions: what, how, when and why people buy things. Solomon et al. (2016) define it as processes in which individuals select, buy, use or have products, services, ideas, or experience at a disposal to meet their needs and desires. Kotler and Keller (2011) emphasize the significance of understanding customers' buying behaviour as well as the ways of selecting products and services that provide a competitive advantage for organizations. Kotler et al. (2012) describe the factors influencing buying behaviour as a cultural, social, personal, psychological factors as well as the customer himself/herself. In the context of selling behaviour, sellers should realize the significance of a whole selling process (Eriksson, 2014;Rein, Purde, 2018). According to Lorincová et al. (2018), the role of sellers is not only taking and acquiring orders, communicating with customers or providing information about products. The key to the success in th trade environment among generations lies in analysing customers' feelings and emotions and providing them with what they need and want (Garton a Fromm, 2013). In general, we can define behaviour as a way that an individual expresses himself/herself or behaves towards others in a society. In the trade environmnent, sellers express themselves by their selling behaviour and on the other hand, there are customers with their buying behaviour and according to Kokemuller (2017), it is just the professional sellers' behavior that is a key to the success. For the