Selling Steam accounts clearly violates the Steam Subscriber Agreement. The Steam web site has a copy of the subscriber agreement and it states in the last part of its "Registration and Activation" section that, "You may not sell or charge others for the right to use your Account, or otherwise transfer your Account." That means that, if they wanted to, Steam's operators at Valve could decide to ban that account.This would leave the buyer out of pocket. Also, a lot of these sellers are scammers. They sell you their account wait for a while then claim their account been hacked, provide Steam with account details and reclaim the account back.
Steam Subscriber Agreement
