Among your switches at Admin Panel -> Settings -> Switches you have an "Revision Requests" option. If someone has submitted something which you don't think belongs on the site, but which you believe they could fix to make acceptable, you can request a revision. The option appears on the admin and moderator validation pages (since WSN 7.1.0) and on the "Edit Comment" page when the switch is enabled. Clicking "request revision" will bring you to a prompt asking you to describe exactly what the person should fix. The submission will become invisible and the member will be notified via private messaging or email. If they edit the submission, it will then appear on the pending validation page where you can approve or reject the new version. The moderator who requests the revision will be notified of the completed revision via PM or email.