I think you should make it so Premium users can view other users warning level. I'm quite nosey, and seeing what others are warned for could be beneficial, say it's for "Scamming another user" We'll know to trade with caution.
With saying that, it brings up another idea. If a user is caught scamming,admits to it, and returns the goods or service of which he scammed I believe they should get a symbol next to there user name such as "Scammed" or "Trade with caution" to notify the user that the user they are dealing with is an ex scammer.