There are a few theories on alignment. Thomas Hobbes said that all humans are innately evil, but do good because it's what society dictates. Calvin said that humans are innately good, but are prone to evil acts. Whatever your view on this, there's a way to exploit being a bad person.
One of the most recent tricks is to sell Fortune Cards. Not Mysterious Fortune Cards, but the Fortune Cards that have already been flipped. These are not Soulbound, and thus can be put on the AH. Unsuspecting players will buy them out, only to find out they basically bought vendor trash. Even more devious still is to advertise them in Trade Chat, saying that you could win big from them, and put them up at a fraction of the price of the current cards. Players will immediately rush to the Auction House, shift click the name in the Trade Chat, and buy them out.
The old trick, which is now obsolete, is posting stacks of Ice Threaded Arrow in the AH for less. The trick is you don't post a full stack of 1,000, you put maybe 100, or 10. Most players won't notice, and buy them out. Alternatively, you could post 500 arrows individually (10 pages), but this is more of an annoyance tactic.
Something more sneaky that you can do is hop on an alt, and post in trade "WTT XXXXX (super rare epic item) for X amount of Embersilk!" When people ask why, just say that you're cutting out the middleman: you need cloth for leveling your profession, and you'd rather just trade the item for cloth. A good way to do this is to make sure the total worth of the cloth is around 2/3rds the value of the epic. "Savvy" players will quickly realize the deal, run to the AH, buy all the cloth, and whisper you. The sneaky part is that you already purchased all the cloth on the AH and relisted it for slightly higher prices (under a different alt), so they're just buying out your auctions. Profit! But we're not done yet. You know that epic that you're trading for all this cloth? You don't even have it. When you get a whisper, "hey I have all the cloth where should I meet you?" just respond "Oh I'm sorry I already traded it, thanks anyway." Log out, delete the toon, and you got a ton of gold.
One more thing that you could do, although this is a hit or miss, is ask people to CoD you things. Some newer players may not know that you need to change the radial button on the mail pane to use the CoD option. Just tell them to send you the item, put the amount of gold you're paying them in the gold box, click "Send" and then "Yes." They may not fall for it, or they may know to change the option to get it to be a CoD instead of just sending you gold, but you never know. There are some not very bright people out there.