Investors use the bond ratings from Moody's, S&P, and Fitch to determine which bonds they will buy and the prices they are willing to pay for them. The rating services charge the firms and governments that issue bonds, rather than investors, for their services. Critics argue that the rating agencies may give higher ratings than are justified in order to continue to sell their services to bond issuing firms. To avoid this impression, why don't Moody's, S&P, and Fitch sell their services directly to investors?