I have amended /skin/_item.feedback_inc.php to only show the option to allow feedback if the user is logged in and user level is greater than 1.

line 353: insert new line
if(isset($current_User) and ($current_User->level)>1){

old line 353 now line 354: add closing bracket to end
skin_include( '_item_comment_form.inc.php', $params );}

Added the file to /skin/elf_zen/ in calstock.org.uk and rogerlovejoy.net