I don't think you have experienced an MMO destroyed by gold sellers. Anybody who played **** can tell you they own entire areas of the game. Quests can't be completed and resources can't be harvested because scores of gold farmers choke entire areas.
I also played WoW and both my wife and I never bought gold but had each of our accounts compromised and everything taken from us and used to fuel the gold selling machine.
These are things that will happen no matter what of course but if the community works together as they do in LOTRO where gold selling is a minor problem, because the community rejects them and reports them, then we can nip the problem in the bud as much as is possible.
But what can Cryptic do apart from acting on reported players?
Every game has this issue, and sure there are ways to stop them, but that would mean remove exchange from the game, ban all energy trade (even within fleets).
It is a fine line between doing what you can to stop gold/energy traders, and restricting it too much so people get annoyed at that as well. It is not a black and white thing.
I do not have any suggestions to how to fix it apart from reporting players that do sell, and hopefully that will be enough. (but no mmo i know of has managed to successfully stop gold / energy / credit sellers 100%)