In this diploma thesis we deal with a specific method of market research called Mystery shopping. The thesis is divided into two parts: theoretical and practical. The theoretical part deals with marketing research and its methodology and discusses the theoretical background to the selected issue of Mystery Shopping. The thesis presents the results of quality evaluation of services provided in selected Nay stores through the Mystery shopping method, in which we focus on selected aspects (exterior, interior, staff and their approach to the customer) affecting overall customer satisfaction. In conclusion we bring suggestions for improving the quality of the currently provided services.