The Selling of Steam accounts goes against Steam's TOS: http://store.steampowered.com/subscr...ement/?l=dutch. Therefore anyone caught doing so may be punished.

"You may not sell or charge others for the right to use your Account, or otherwise transfer your Account, nor may you sell, charge others for the right to use, or transfer any Subscriptions other than if and as expressly permitted by this Agreement (including any Subscription Terms or Rules of Use)."