cant you easily get back your account after selling it by writing to steam and telling it was stolen?
I also suspect that is the case, if the seller wishes to do so.
According to "Reclaiming a Stolen or Hijacked Steam Account", from Steam Support, to recover the account, the seller would need the original email address used to register the account (though I imagine one can claim it was hacked as well), and proof of ownership, in the form of Credit Cards or Bank Transfers associated with the account, CD Keys, or Steam Wallet Codes. All in all, this seems a risky trade.