I know at least two people that have bought RuneScape gold. One bought 1m in gold for around $15 and another I know bought around 4m gold... not sure how much, but they did. I don't blame them. But I would never do it either. I've made a total of around 3.5m total (probably that and more not counting my losses). That's not bad for a f2p.
But I digress. Those two have never been caught. They have both been active as well. RuneScape acts as though if you buy the gold, you WILL be banned. That's not necessarily so. I think that if RuneScape wanted to stop people buying and selling gold in real life, they'd ban the macroers as well as those whom they sell to. Those things are everywhere. I'm not kidding... I'm sure you've seen them. Cutting Yews, fishing lobbies and swordies, in the mining guild and crafting guild. It's irritating to see them knowing RuneScape might ban some of you (a very small amount of you) and let these autoers go free...
Hm... I wonder what those people do with their accounts once their done with them...