The IRS can audit you by mail, in the IRS offices, in your office or in your home. The location of your audit is a good indication of the severity of the audit. Typically, correspondence audits are for missing documents in your tax return the IRS computers have attempted to find. These usually include W-2's and 1099 income items or interest expense items. This type of audit can be handled through the mail with the correct documentation.
The IRS office audit is usually with a Tax Examiner who will request numerous documents and explanations of various deductions. This type of audit may also require you to produce all bank records for a period of time so the IRS can check for unreported income.
The IRS audit scheduled for your home or office should be taken more seriously due to the fact the IRS Auditor is a Revenue Agent. Revenue Agents receive more training and auditing techniques than a typical Tax Examiner.
All IRS audits should be taken seriously because they often lead to an audit of other tax years and other tax deductions not originally stated in the audit letter.