It is quite common for large gold-selling sites to do this once in a while, and to be honest, they can get away with it.
Buying gold/items is already illegal to begin with. You think suing them for something illegal will get you what you want back? That's the equivalent of getting some other shit mixed in with some drugs you illegally bought, then wanting to go to the cops for it -- you'd be stupid to do so.
Selling gold and items is also illegal, don't you think they know that? They are a (somewhat) established company, they have been up for so long, you don't think that they can get away with this sort of thing?