In order to fully inform the buyer about the comprehensive and successful exercise of his rights in cases of defects in the purchased item, the article provides an overview of the rules of liability based on the issued guarantee for the correctness of the sold item. Since the customer often encounters confusing information about how to act if the purchased item turns out to be defective, the purpose of the article is to be somewhat of a guide for customers in such situations. The emphasis is on the rights and obligations arising from the guarantee certificate, with a brief overview of the relationship between the institute of liability for material defects and liability under the guarantee, i.e., the guarantee in the introductory part of the article.