The reliability of non-destructive evaluation depends on multitude of different factors. Consequently, it is difficult to assess the performance of the system. The only practical way to overcome this complexity and asses inspection reliability is using practical trials. In practical trials the inspection is performed on a known, flawed sample and reliability is judged by comparing the acquired inspection result with known state of the sample. However, confirming (and demonstrating), that the practical trials and, in particular, the used flaws are representative to postulated inspection case is, at present, challenging. In this paper, the open literature is reviewed and compiled to the extent necessary for providing a starting point for confirming and demonstrating representativeness of flaws used in the practical trials. The available information on essential flaw parameters for various NDE techniques is reviewed. The used measurement methods for each parameter is discussed and the available in-service data summarized. Finally, a simple procedure is proposed for confirming and demonstrating the representativeness of used flaws.