What to Do If You Get a Sales Tax Audit

How Sales Tax Audits Are Triggered

States select businesses for audit through several mechanisms. Random selection is relatively rare for small online sellers, as states prioritize their audit resources toward higher-revenue targets. More common triggers for ecommerce businesses include filing patterns that indicate potential issues (large fluctuations in reported sales, consistently reporting zero or very low tax due, stopping filing without closing your account), data matching where a state compares marketplace data (from Amazon, payment processors, or 1099-K reports) against your filed returns and finds discrepancies, industry targeting where a state focuses audit resources on specific industries or business types (ecommerce is an increasingly common target category), and tips or referrals from competitors, former employees, or other states.

States also conduct "nexus audits" where they identify out-of-state sellers who appear to have nexus in their state but are not registered or collecting. These are typically initiated through data sharing between states, analysis of marketplace transaction data, or review of businesses advertising or shipping to in-state customers. A nexus audit is different from a compliance audit: the state is establishing that you should have been collecting, not reviewing whether your collection was correct.

What the Audit Notice Looks Like

An audit begins with a letter from the state's department of revenue or comptroller's office. The letter identifies the audit period (typically 3 to 4 calendar years), the records the state wants to review, the name and contact information of the assigned auditor, and a deadline for producing records, usually 30 to 60 days. Some states conduct desk audits (reviewing records you submit electronically or by mail) while others conduct field audits (an auditor visits your business location or schedules video conferences to review records in real time).

Do not ignore an audit notice. Non-response leads to the state issuing an estimated assessment based on whatever data they have, which is almost always higher than what an actual audit would produce. Estimated assessments assume the worst case, and the burden shifts to you to prove a lower amount through an appeal process that is more difficult than cooperating with the original audit.

Records the Auditor Will Request

A sales tax auditor typically requests sales records for the audit period from all channels (ecommerce platform data, marketplace reports, point-of-sale records), sales tax returns filed during the period, bank statements showing deposits for the audit period, exemption certificates for all tax-exempt transactions, purchase records (to verify use tax on business purchases), and your chart of accounts and general ledger entries related to sales and sales tax.

For ecommerce businesses, the sales records request means exporting order data from Shopify, WooCommerce, Amazon Seller Central, and every other platform where you made sales during the audit period. The auditor will compare your order-level data against the sales totals reported on your returns. Any discrepancy between total orders and reported sales triggers deeper investigation.

Common Audit Findings for Ecommerce Sellers

Missing exemption certificates. The most common and often most expensive audit finding. Every tax-exempt sale on your return needs a valid exemption certificate on file. Sales without certificates are reclassified as taxable, and you owe the tax plus interest. If 10% of your sales are exempt but you only have certificates for half, the other 5% becomes taxable liability. See our exemptions guide for proper documentation practices.

Unreported sales. If your ecommerce platform shows $500,000 in sales to a state during the audit period but your returns only reported $400,000, the auditor will assess tax on the $100,000 difference. Common causes include failing to include all selling channels in your return data, incorrectly excluding shipping or handling charges from taxable sales in states where they are taxable, and mathematical or data entry errors on returns.

Incorrect product taxability. If you sell a product that is taxable in a state but classified it as exempt in your tax settings, the auditor will assess tax on all sales of that product. This is common with products that are exempt in some states but taxable in others, where a seller applies the wrong state's rule.

Use tax on business purchases. States also review whether you paid sales tax or accrued use tax on products purchased for your own business use. If you bought office equipment, packaging supplies, or software from out-of-state vendors who did not charge you sales tax, you likely owe use tax in your state on those purchases.

How to Respond to an Audit

Respond to the audit notice within the stated deadline. Contact the assigned auditor to acknowledge receipt and discuss the timeline and format for providing records. If you need additional time to gather records, most auditors will grant a reasonable extension if you ask before the deadline passes.

Organize your records before submitting them. Well-organized records demonstrate compliance effort and make the auditor's job easier, which generally leads to more favorable treatment on judgment calls. Provide records in the format the auditor requests (typically electronic spreadsheets for transaction data). Include a summary cover sheet that reconciles your reported sales to your order data, explaining any known discrepancies.

Consider hiring a CPA or sales tax attorney to represent you in the audit, especially if the potential liability is significant. A professional who regularly handles sales tax audits knows how to present records favorably, negotiate with auditors on gray-area issues, and challenge incorrect assessments. The cost of representation ($2,000 to $10,000 depending on complexity) is often recovered through reduced assessments.

Negotiating the Assessment

After reviewing your records, the auditor issues a preliminary assessment showing the additional tax owed, penalties, and interest. Review this assessment carefully. Auditors make mistakes, and you have the right to dispute findings you believe are incorrect. Common reasons to challenge an assessment include the auditor reclassified exempt sales where you actually have certificates (provide the missing certificates), the auditor used sampling methodology that you believe is not representative of your actual sales, the auditor applied incorrect tax rates or product taxability rules, or the calculation includes mathematical errors.

Most states have a formal protest or appeal process. The first step is typically an informal conference with the auditor and their supervisor to discuss disputed items. If you cannot resolve the dispute informally, you can file a formal protest with the state's administrative hearing office or tax appeals tribunal. The protest process adds time (3 to 12 months) but can significantly reduce an assessment if you have legitimate grounds for disagreement.

Preventing Future Audits

The best audit defense is accurate, well-documented compliance. File every return on time and accurately. Maintain organized exemption certificate files for all exempt transactions. Reconcile your order data against your return data each filing period. Use sales tax software with accurate rate calculation to minimize taxability errors. Keep all records for at least 4 years (the typical audit look-back period, though some states can look back further in cases of fraud or significant underpayment).

After completing an audit, implement any process improvements the auditor identified. If the audit found missing exemption certificates, build a certificate collection process into your sales workflow. If it found unreported marketplace sales, verify that all channels are connected to your tax reporting system. The same issues that triggered one audit will trigger the next one if they are not corrected.