As private rating agencies live on the fees they collect from rated companies, they cannot easily downgrade important clients or the assets they sell. The big American investment banks received excellent ratings up to the last moment, and so did the CDOs with which they betrayed the world.
CDOs的买家往往被行为不良且提供不了可靠信息的评级机构所误导。至于靠收取被评估公司费用生存的私人评级机构，它们不能轻易对重要客户或所出售的资产给予降级。美国最大的投资银行直到最后一刻仍获得良好的评级，它们用来欺骗世界的CDO也受到同样优秀的评级。