Online sales portals are commonly used to commit fraud. Specific methods of perpetrator’s operations vary, depending on the available functionalities of a given sales platform and specific features of targeted victims. However, there are several common elements of modus operandi shared by most online fraud perpetrators. These elements have a direct impact on the potential effectiveness of the investigative process. This presents the typical elements of modus operandi of a perpetrator of a fraud committed online via sales portals. The description is supplemented by a specific list of the existing investigative problems and potential methods of solving them. Presented practical information is illustrated with up-to-date data on the scale of the occurrence of such acts based on statistical data analysis and an analysis of criminal cases files.