Last month, four insider executives within ExOne (XONE) sold off a total of roughly 1.5 million shares of the company's stock, to the tune of $88.4 million. Should investors be worried that something is fundamentally wrong behind the scenes? In this video, Motley Fool industrials analyst Blake Bos discusses why this move was to be expected, and why it could be another sign that the stock is a bit overvalued.