Goto the admin feedback forum:
http://eq2.allakhazam.com/forum.html?forum=3
Make a post with a simple header such as "RMT post in EQ2 forum", "Platseller on EQ2 forum" etc. Provide links to the offending post, name of poster. Then wait for the admins to nuke the post and ban the account post haste.
Example.
No need to flame, get upset or screaming bloody murder. Admins usually have it gone as soon as they see the post.