Academic paper from 2016 by Vita Faychuk, abstract includes “… Municipal bonds are extremely heterogeneous, municipal financial reporting is opaque, so the cost of acquiring and processing information is very large for a non-professional municipal investor. As a result, individual investors rely excessively on credit ratings as a convenient credit risk summary. This is especially worrying, taking into account the quality of credit ratings that has raised a lot of questions in the aftermath of the 2008-2009 financial crisis. It is even more problematic given the fact that the credit rating agencies claim no legal responsibility for the quality of information they provide.”