I've read a report, that in China there are a lot kids, which can play for free to make as much money as possible and the guys, which offer this kind of service are selling this WoW Gold on ebay-like plattforms.
Crazy stuff... really!
I was real life friends with someone who purchased WoW gold. I was in the same guild with him and spent a lot of time raiding with them to get us to a decent content level. Then he goes and does something completely stupid and buys 5K WoW gold so he can farm more effectively on an epic mount. I quit that guild and server thereafter. I have no time or respect for people who support a this type of thing. Those gold sellers are often the same ones hacking accounts.
I've seen it where they try to charge to power level a character for you to a certain level. The problem with this is they usually hack on the character so it's not really worth doing, also your character will never be considered legit if anyone finds out. I say just stay away from crap like that, it's a game and it's supposed to take time to get to a certain level and also it just feels much better when you do everything yourself.