1. Goldman-Sachs has its own trading desk. But majority of its profits comes from investment banking--underwriting. Goldman Sachs is a broker too. Its analyst can upgrade or downgrade a stock. Other institutions can subscribe services from Goldman Sachs. Goldmand Sachs wins commission business from those institutions (mutual funds and hedge funds).

2. Big institutions such as Fidelity can move a stock easily. However, they are not brokers, so they cannot upgrade or downgrade stocks. Otherwise, we have no way to play the game.