Reporting no-shows should only be used in cases where an user fails to communicate prior to the start of the session that he will not be attending the session. If the user leaves the session prior to the start time, that is not worthy of a no-show report.
However, reporting users as no-shows is important to help keep the site functioning as intended.
To mark someone as a no-show, go the gaming session and click mark as a no-show. More than one user must mark them as a no-show to prevent fraudulent activity.