After a player complains that they mistakenly paid 75g for wool cloth in the Auction House, Drysc confirms that Blizzard is all about caveat emptor: the auction house market is all about open trade, so if you buy something for the wrong price, it's all on you.
This, of course, leaves the system fairly open to rampant fraud -- I know someone on another server who would often buy anything epic on the AH, day in and day out, and inflate the price an extra thousand gold. In many cases, the free market (which I'm pretty sure this is, right economists?) can usually correct itself -- you have to stay on top of a certain market if you plan to dominate it, since if anyone posts a lower price than you, you'll lose out on a sale. But in terms of a fraud -- the original poster in the thread claims that no one would ever have a serious reason to sell wool for 75g -- it's always "be careful what you click." Blizzard isn't completely laissez-faire when it comes to the economy, of course; they control the flow of gold in all kinds of ways. But when it comes to the auction house, you're on your own.