Sales tax is administered by each state, and audit procedures, look-back periods, appeal rights, and penalties vary widely. This article describes common patterns. For your state, check the revenue department's audit guidance and talk to a qualified adviser. Nothing here is specific to any one state.
A sales tax audit letter lands differently than an IRS letter. It is usually from a state department of revenue or comptroller, the questions are narrower, and the auditor often has real leverage because the tax you collected belongs to the state. The best defense is organization.
Why businesses get audited
- Reported taxable sales that look low compared to your industry or to other filings, such as income tax returns.
- Large or frequent exemption claims, especially resale and exempt-customer sales.
- Registered but not filing, or filing zero returns despite activity.
- Third-party data, such as marketplace reports or payment processors, that does not match your returns.
- Random selection or a prior audit with findings.
- Industry programs targeting restaurants, retail, construction, or online sellers.
What auditors typically examine
- 1Sales: whether all taxable sales were reported and the right rate was applied.
- 2Exempt sales: whether you hold valid exemption or resale certificates for each exempt transaction.
- 3Purchases: whether you paid sales tax on items bought for your own use, or owe use tax on purchases made without tax.
- 4Taxability decisions: whether products or services were treated correctly.
- 5Reconciliation: whether returns agree with books, bank deposits, and income tax returns.
- 6Registration and nexus: whether you should have been collecting in other states.
Records to assemble
- Sales detail from your POS, platform, or accounting system for the audit period.
- Filed sales tax returns and proof of payment.
- Bank statements and payment processor reports to tie sales to deposits.
- Exemption and resale certificates, organized by customer.
- Purchase invoices for equipment, supplies, and inventory.
- Chart of accounts, general ledger, and income tax returns.
- Contracts and invoices that show how taxable and exempt items were separated.
Sampling and projection
When records are voluminous, many states audit a sample of transactions and project the error rate over the entire period. A small error rate in the sample can produce a large assessment. Agree on a sampling method only after you understand it, and offer complete records where you can. Good records often reduce or eliminate the need for projection.
Exemption certificates are the usual weak point
If you sold without tax to customers claiming an exemption and cannot produce a valid certificate, the auditor may treat the sale as taxable and assess tax you never collected. Collect certificates at the time of sale, check that they are complete and current for your state, and keep them for the period your state requires. See sales tax filing services.
How to respond
- 1Read the notice for the audit period, the documents requested, and the deadline.
- 2Do not ignore it or miss the first appointment. Ask for more time in writing if needed.
- 3Get your books reconciled to returns before the auditor starts. See bookkeeping cleanup services.
- 4Provide what is asked for, organized and labeled, and keep copies.
- 5Consider appointing a representative with power of attorney for the state agency.
- 6Review the auditor's findings carefully before you sign anything.
If you disagree
Most states offer a review or appeals process after the audit findings, often with strict deadlines, sometimes measured in days or weeks. Ask what your state's process is before you sign an agreement to the results. Some states also offer penalty waivers or payment plans for audit assessments.
If the audit finds you should have registered elsewhere
An audit can uncover nexus in states where you never registered. In some states you can request voluntary disclosure before being contacted, which may limit look-back and penalties. Once a state contacts you, those options may narrow. See multi-state sales tax compliance.
Mistakes that increase the bill
- Unorganized records that force the auditor to estimate.
- Agreeing to a long statute extension without understanding it.
- Offering information beyond what was asked.
- Missing certificates for exempt sales.
- Ignoring use tax on purchases.
- Treating sales tax collected as business cash.
Our sales tax compliance service helps businesses prepare and respond to state audits. To talk about your sales tax compliance, tell us which state sent the notice, the audit period, and what was requested. Outcomes depend on your records and your state's rules.
