Heh, I destroyed a server economy once, and did it legitimately by playing the AH fairly well on a small server. I never got banned for it, despite being told by a GM that what I was doing was "morally wrong" or something similar to that.

One day while sitting in my advanced economics class looking at my WoW auction house app, I got a brilliant idea to not only monopolize the gem market but to also collude with other gem cutters to not sell their gems below a certain market price. Anyone who undercut other sellers were immediately purchased and resold at the above the colluded minimum price.

I should mention at this point that the "colluded minimum price" was over 300g higher than the market value of the gems. So a gem that would normally cost 50g would be listed at 350g and everyone else would be pricing them exactly the same.

Some sellers who didn't play along would place the gems at the listed value of 50g, and one of the people who were cornering the market would buy them up and re-list them at the 350g price. People were of course stupid enough to buy the 350g price -- but that wasn't the point.

The point and reason that the market crashed would be because the gems would be "reset" to a higher market rate. Someone would come in with Auctioneer or whatever it was, and undercut everyone by 1c. Now, even the auto sellers who weren't colluding were selling gems in the 300g ranges.

Because of how WoW markets work, people were asking gem cutters to cut gems for them in trade, but because we had collusion most of the cutters would only cut for market rates (i.e. uncut gem costs subtracted from the cut gem price).

This resulted in the price of ALL items increasing by a significant amount -- crashing the market because people had a hard time affording most of the mats if they weren't in a large and functioning guild.

So worth the 3 months of my life.