Unless you have studied tax law or have been audited previously, you probably have no idea how an audit works. Audits typically start with the IRS asking for documents and other information that supports what you claimed on your tax returns. You may believe that what you are providing or the information you are missing is innocent, but the IRS and State will focus on information that gives them permission to disallow your expenses. When an expense is disallowed it turns into income which you will owe taxes on dating back to the year the tax return was due and compounded with penalties and interest over the time period that has passed. This is why tax audit representation can be necessary to ensure you are protected. An IRS tax representative with audit experience will prepare your information in a well-organized package that is annotated with explanations and fight for your rights.
After the audit is complete, the IRS will present their findings and proposed results and will most likely have found that you owe money. If you get to that point, your IRS and CPA tax audit representation can help you contest the findings and file an official tax court petition on your behalf.