When someone says they aren't willing to pay so much or sell for so little, we understand it's just haggling and don't assign it much weight. I'm more concerned about stock markets and similar setups, like decision markets, where the incentives are to lie to the general public, including uninvolved third parties, rather than to a specific business partner. I was struck by this interview (starting at about 7:30), in which a hedge fund trader admits to spreading false rumors about companies in order to profit from the effect on their stocks. Some traders are very good at taking advantage of brief oscillations in price, so this strategy is viable even if the market quickly restores the stock price to its correct value.

(This is also why I don't think decision markets and prediction markets are a good idea. The information provided by the market's price is greatly outweighed by the lies traders could spread to make that price oscillate.)