what about a form of stock market where one can buy shares in rival companies to try to get majority share? example Plutocracy. ...which opens some management options to perhaps influence their policies to not compete or conflict with your market share.
To make share-buying harder one might need to befriend/seduce some shareholders/owners first to allow buying their portion of shares (like the carwash storyline) so players dont just throw cheated money at the problem. Also get potential ROI naturally from that sharing profit.