Well, in a perfect world, code would be glorious and always bug free. Any bugs that somehow DID creep in, due to data corruption or w/e wouldn't be exploited by the players. And thus both sides meet in the middle.
Obviously this isn't a magically perfect world. And they can only work on the code side.
I wish to all the gods that there was a way to train your playerbase to not be asshats. But between lack ability to implement in-game controls, fear over driving away customers, general "customer is always right" United States mentality, our growing "it's only illegal if you get caught, and then you simply pay your fines and move on to your next scheme" trend; civil and civic mindedness (in games) are fucked.
still, knowing all this, it really surprises me that games don't have robust, long term logging, with automatic flagging of strange behavior. It can be as simple as "earn more than X exp/min", " X coin/hour gain", "highest/lowest auction house listing prices in the last day". It may take a week or two of tweaking the numbers so that normal transactions don't flood the flagged list, but all of those, at worst give you solid insights into how your world is working, and at best highlight potential shitstorms.
"Why are we seeing negative number bids in the AH?"
"Why are we seeing all these solo runs on top level dungeons?"
"Why are we seeing this 800000% over the average player spike in cash/hour earned for these 4 players ?"