Retail companies operate in a highly competitive market. Marketing specialists should focus their activities on keeping customers loyalty on a high level, which is critical to achieving success in the retail business. The efficiency of marketing campaigns impacts the performance of the whole business directly. Electronic channels of customer contact help in gathering massive data sets describing customers and their behaviour. Companies can use the data to gain knowledge about their customers and valuable insights about patterns of customer behaviour. Such knowledge enables the application of actions improving the loyalty of customers and satisfaction of customers. This paper elaborates on customer loyalty and shows how to use data in marketing and sales processes in retail. Authors present a method of advanced data analysis based on machine learning techniques to generate tailored offers for clients applicable in an eCommerce company.