First off great Idea no more spam in that area.
Ok well I noticed that you also applied this rule to the Account Training section, this could pose some problems. Inx has a recent post where he is asking how much it would cost him to get 99 cooking trained. While he could wait for a Offical Trainer to come by and tell him the price per xp a regular member could come along and tell him that very same info in half the time.
Just sorta my little rant because I can't answer questions in there anymore.