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?Let's take a look at what these Wall Street heavyweights have to say about Costco (COST) before we discuss the reliability of brokerage recommendations and how to use them to your advantage.Costco currently has an average bro ...