Why bother opening up a crown sink or regulating the energy market when you can just remove all of the excess crowns and energy in one fell swoop by banning merchants for no factual reason? The terms of service clearly state that you can ban people for any reason at all, and many of these players don't even value the efforts put into prize boxes. That alone should be grounds for a ban.
Developer effort: Zero
GM effort: Negative, as they would gain enjoyment from banning these players.
While you're at it, why not ban everybody who complains about prize boxes? Don't want them in Spiral Knights? Well too bad, because its either boxes or no game.