hmm, although trading is a pretty nasty thing.. micechat clearly states: MiceChat is not responsible for lost items/credits due to trades. Be sure to check our feedback system.
so unfortunantly, there is nothing that can be done about this, you should however, give him feedback so other players will be aware of this when trading the person.
also, personal attacks are also not allowed, and may result in suspensions or closed threads, bans.
so play nice, and next time you trade, be sure to check the players feedback and make judgements accordingly.