The goal of the present paper is to draw attention to some key rules and principles of the purchase contract. After the specification of this contract type we will deal in more details with the defective performance and the procedure of its complaint. As suggest the first assessment and reviews of the application of new legislation in its practical use and by the case law, in the achievement of the objective desired by the NCC - to increase the transparency of the procedure of complaints – the new legislation stacked in the middle of the way. The paper compares the impact of the new the previous and the current regulations, We will use the method of functional analysis as well as the method of legal formalistic comparison. It is obvious that the new rules respect the former régime of commercial contracts. The business sphere has undoubtedly welcomed this feature of the legal regime as the merchandisers are familiar with this rules. The second issue is, however, how this modification in the general regulation meets the expectations of the to provide sufficient legal certainty in the interpretation of contractual provisions and in the access to the protection of their interests by courts in the event of disputes