People should be able to put bound items in the trade box, but if somone does, he must additionally confirm the warning "it is bound. all heat will be lost blah blah blah". The other player will then get a message about the unbind fee and must enter enough energy to unbind it to complete the trade.
That way sellers have no reason to ask others to pay unbind upfront, which can be used as an excuse by scammers to get energy.
Also sellers have no risk to pay to unbind an item (and lose its heat) that the buyer then refuses to buy.
I actually really like this. One thing I would make unambiguous though is that the regular unbinding smith in the Bazaar doesn't disappear. I'd like to have both options, but for those that play the market this would make trades safer.
Maybe add the option to put "unbind fees" on auction house items if the item was previously unbound at Vise? Would be another way to trade CE.