Market orders are relisted every ~10mins at the market price until fulfilled. If you want to sell at no less than some $X, that's what limit orders are for. You

Market orders are relisted every ~10mins at the market price until fulfilled. If you want to sell at no less than some $X, that's what limit orders are for. You used a market order when what you wanted was a limit order; that's not Bitstamp's fault (unless the fault is in making it clear what the difference is, but IIRC they do explain in the FAQ).