Even though its completely immoral, their actually not doing anything to warrant action at the moment.... its the same irl, your well within your rights to try and sell somthing for a ridiculous price as long as the person isnt missinformed about the purchase, as soon as you say somthing that isnt true, thats when action can be taken.
The simple solution to this is to help people make better informed decisions before buying things on the marketplace.... make a feature which clearly states what level heirloom the item is instead of people relying on the name of the item.
