The recommendations of Wall Street analysts are often relied on by investors when deciding whether to buy, sell, or hold a stock. Media reports about these brokerage-firm-employed (or sell-side) analysts changing their ratings often affect a stock's price. Do they really matter, though?Before we discuss the reliability of brokerage recommendations and how to use them to your advantage, let's see what these Wall Street heavyweights think about Merck (MRK) .Merck currently has an average brokerage recommendat ...