We leave no stone unturned when looking for the next great investment idea. For example Europe is set to become the world's largest cannabis market, so we check out this European marijuana stock pitch. We read hedge fund investor letters and listen to stock pitches at hedge fund conferences, and and go through short-term trade recommendations like this one. We even check out the recommendations of services with hard to believe track records. In January, we recommended a long position in one of the most shorted stocks in the market, and that stock returned more than 50% despite the large losses in the market since our recommendation. Keeping this in mind let's review the key hedge fund action regarding Marathon Petroleum Corp (NYSE: MPC ).