The aim of the diploma thesis is to describe in more detail the research method of mystery shopping and the subsequent application of this method in practice in selected company. The final work consists of the theoretical and practical part. The task of the first part of the diploma thesis is a closer explanation of the concept of mystery shopping, mystery shopper and we also deal with the phases of mystery shopping. In the practical part of the diploma thesis we deal with the application of mystery shopping in selected company. Specifically we will focus on operations of Teta Drogérie of which there are several in Zvolen. Regarding the results of the mystery shopping, we suggest recommendations leading to improvement of the provided services in the researched company.