Why was I banned?

My username on here (ReachForAMillion) was banned. When I logged on this is the message I got:



What exactly does this mean I got banned for? .. All I did on my username was attempt to sell a world of warcraft gold making guide that I put a lot of time and effort into making. I posted it in the section that other players were clearly selling guides on how to make gold too. So what exactly did I do wrong that the others didn't?