Sort of unrelated to the matter, but just a fun lil' story:
In the days of vanilla wow, there was this thing called a Black Lotus, used for all the flasks (very important for hardcore raiding). I recall it selling for something like 15 gold each on my server, fair enough. When I decided to migrate to another server for a new guild with friends, I got this idea to scout out the ah and see how the prices differed. Well, I noticed that on that server, the BL sold for around 30 gold. Cool, I thought, I'll make some money with those.
So I spent almost 5000 gold buying Black Lotus on my old server, and when I migrated, I almost doubled my money selling them away.
And in those days, that was a HUGE amount of money. Back when most people could never afford an epic mount for around 800 gold. Needless to say I was pretty much set for life. So there are some fun ways to "exploit" the auction houses in mmorpgs.