You have filed your taxes and are awaiting your return. Instead, you receive a letter, notifying you about a pending audit or investigation. A surprisingly high number of people in this situation make the decision to represent themselves in the investigation.
Most average citizens do not have any experience in IRS audits and negotiations. Because of this, they cannot understand the value of hiring an accounting professional who has the knowledge and experience required for a successful outcome.
In the down economy, many people are in a position where they are unable to pay their tax liability. Despite this, they work with the IRS to set up payment plans they know that they cannot make good on. As a society, we have been bred to loathe and fear the IRS, so it is not surprising that many taxpayers in this situation simply roll over and take whatever deal they are offered by the IRS.