Unlike most investors, short sellers make money when the value of a company falls. And they don't have a great reputation. They're often regarded as the vultures or hyenas of the financial world, preying on weak companies, and sometimes spreading negative rumors to bring a company down.
But quite often, short sellers perform a necessary task. They have a financial incentive to expose weakness and uncover the truth about a company's status. And when they do so, honestly and transparently, the market benefits.