With in-person audits, though, it's often in your best interest to hire a CPA or tax professional to assist you -- unless you're very confident in your tax knowledge.
"It's best to have someone who understands and is able to explain what you did and why you did it," said Lieberman.
6. Pay up.
If you end up owing extra money, you'll get a bill in the mail that's typically due within 30 days, unless you ask to set up a payment plan. If your federal return ends up being changed, you'll typically have 90 days to amend your state return as well.
Disagree with the outcome of an audit? Ask to talk with a manager, who can conduct an internal review. If that doesn't help, you can request assistance from the Taxpayer Advocate Service, the IRS's watchdog arm. As a last resort, you can appeal the audit in U.S. Tax Court, a federal court specializing in tax cases.
But these avenues can be time-consuming and expensive, so make sure the fight is worth it, said Lieberman.