An audit is a good time to have a tax attorney on your side, especially if you're a business owner. The Internal Revenue Service is single-minded in its attempts to collect what it sees as tax shortfalls, and an attorney can prevent them from taking advantage of you.
Remember that anything you reveal to an attorney -- even a tax attorney -- is utterly confidential and can't be revealed to anyone else without your permission. That being the case, be as straight with them as possible, and don't keep anything hidden; you never know what might help your case.