My favourite hacks in trading have always been of the non-technical variety. For instance I remember reading of someone making an absolute fortune on the Diablo

My favourite hacks in trading have always been of the non-technical variety. For instance I remember reading of someone making an absolute fortune on the Diablo 3 auction house, because you could list items on it either for in-game gold or real money. But some people have quickly noticed that it's very easy to make a mistake and list something for 5 gold instead of 5 dollars, and people have in fact been doing it. With a bit of automation(buy anything worth less than X gold and of legendary rarity), people have made an absolute killing, tens of thousands of dollars a month just buying items for cheap and selling them for more. A little bit scummy, but no technical hacking needed, just a simple observation that the UI design of the auction house makes this kind of mistake really simple to make and no checks have been implemented to prevent it(no "this is a legendary item and you're listing it for 5 gold - proceed?").