Until now wow has been mostly microtransaction free. Yeah a lot of people buy gold and the occassional mount but that isn't that game breaking just an economy issue. However there has been ample opportunity for micro transactions to be implemented and cut out the middle man of players that make a side hustle with it. Here is what I expect to really see from the buyout
10 extra loot rolls for 5$
<Insert farmable resource here> 1$ a stack
Experience buffs 1$
etc etc