Lol i have been doing that for a long time. You just have to make sure that the item is desirable enough that more than one person will bid on the item. Other wize you will get ripped off.
Also when two peeps in the bazaar are selling the same item i /action Want to buy (insert item here). Imedeatly i get tells from both and i play them both to get a permium price. Tell who ever sends you a tell first that you would like to buy the item but, (other guy selling the products name) is willing to sell it to me for (insert lie here). Some times it doesn't work but often it does. Just do the same thing to the other guy and who ever gives the lowest price wins =D. You have to know how to make it sound like you have many options open so that they feel like they need to sell the item now while the oportunity is there =).
A good line to use when you want a lower price than what he is trying to sell it for.
"well, i think i am gonna pass for now, i am gonna keep shopping"
Most people will jump at a chance to sell expensive items because it takes forever to finnally get a person to buy it. so when someone wants to buy it.... you know the rest =P