In other words, you have discovered WoW's noble economy
Be careful with excessive buying out and reselling, this can actually get you a suspension as it falls under the compromising realm economy. I am not talking about a few buyouts though, for example people sometimes buyout the whole market of Copper Ore, then the resell it all at an obscene price, all the while buying out any new ones that do not meet their price criteria. For that, Blizz can intervene. Especially if you are gouging those prices as they get complaints from other players. It happens alot more now due to epic mount money also.