Several good points. But no idea alive will stop them save this one: Find their IP. And Nuke their House. Once one city is down people will be using peer pressure along with fear to stop them.

kk that's over extreme (I do like overpowering things that I hate with super mean power) but its as good as all the other ideas. XD Like someone mentioned and as mentioned in OP's post simply can be circumvented and thus exploited by the Sellers. SE's idea to allow us to not trade among our charas was pointless. (And I circumvented that one by having a FC and a few family members who play as well. [Insert family with trusted friends and you too can have two chara sharing most of the stuff you want to share.])