Just thought of this, I read it a while ago (back in 2005 when it was a new phenomenon) but my recent interest in looking into the effects of real money trading (RMT) in multiplayer online games revived interest in these articles.
They're quite long, so if you're interested in social effects of MMORPGs on humans, set aside some time.
The original site is long gone but I found a mirror here:
The Great Scam - EVE Online Gamble your life away on ZT Online As for the actual topic of real-money trading...
How Organized Crime Begins on Professional RMTs This is a blog article in 2006... it's funny that his predictions are so casual, actually. The problem is not that people "buy items" and that farmers take mobs away from legitimate players in the game. It's actually a much larger and more expensive problem as elaborated in the video below:
How Secondary Markets Affect Games (YouTube Video)
For those who don't want to watch the whole thing, the main problem with RMT is that it introduces crime into the game. This is not simply in-game theft of items crime. This is real crime, including theft of personal information by installing third-party keyloggers on your computer.
What often happens is that if you purchase gold, or powerlevelling services, or a bot, you merely visit the web site, and when you click to download an executable file, it will install an undetectable program on your computer that logs keystrokes and transmits them back to a central server. This allows the theft of, primarily, usernames and passwords and in turn allows access not only to your MMORPG game accounts where they can strip your character down, sell all of his items, sell all of the guild bank's items, and then transmit them to the gold farmer of choice, but actually can allow access to your personal information.
Finally, if that all wasn't annoying enough, there's simply the issue of spam. On Aion, it's been reported that over 80% of the chat messages that are transmitted on the server are spam messages. That's a lot of junk.
So what we have is essentially a massive spillover from virtual money into an organized network of corporations who make as much money as they can by promising you virtual gold and in-game levels, and in turn scamming you out of your personal information. As anyone who's ever been hacked can tell you, is it really worth it to buy that powerlevelling service? Even if you don't get hacked yourself, chances are you're supporting the chance that someone else will.
Finally, here's a developer blog entry on just how much of an effect banning bots can have on servers.
Effects of Banning Bots from EVE Online