Floyd Norris had an interesting piece discussing the conflict of interest problems with company auditors and also the bond rating agencies that rate securities issued by banks. The basic problem is that since both are paid by the companies who hire them, they have a strong incentive to give a positive assessment regardless of the reality of the situation. This was a huge problem in the housing bubble years when the credit rating agencies gave trillions of dollars' worth of mortgage backed securities top investment grade ratings even though they were filled with dicey mortgages.
In fact, there is a relatively simple solution to the conflict faced by bond rating agencies which actually was put forward as part of Dodd-Frank. Senator Franken proposed an amendment, which was approved overwhelmingly in a bi-partisan vote, which would have had the Securities and Exchange Commission (SEC) pick the credit rating agency. (I worked with Senator Franken's staff on designing this plan.) This plan would have eliminated the conflict of interest since a negative rating would not reduce the probability of being hired for further work.
This amendment was stripped out in conference committee, with the support of the Obama administration, as Timothy Geithner indicated in his autobiography. The argument against the proposal said a great deal about the corruption underlying the debate on this issue.
The concern was supposedly that the SEC might choose a rating agency that wasn't qualified to rate a particular issue. The absurdity of this concern should be apparent on its face. The SEC would not be sending Bozo the Clown to rate these issues, they would be sending professional auditors. Of course the correct way for a professional auditor to respond if they see an issue they don't understand is to say that they can't rate it, which would then allow the SEC to pick an agency that has auditors who can rate it.
However there is an even more basic issue, why are banks securitizing issues that professional auditors can't understand? It is highly likely that if the professional auditors employed by credit rating agencies can't understand an issue then many of the investors who will buy the issue also will not be able to understand it. In that case, it is probably best for the economy that the issue not be marketed.
All of this should be pretty evident on a moment's reflection, but in a world where Wall Street controls the debate on such issues, this simple logic was completely excluded from the debate.