From Reactive to Proactive: The Case for Reverse Audits

Guest Author: Larry Mellon
Senior Director, Vertex, Inc.

When most indirect tax professionals think about compliance, the focus often lands on sales and use tax assessments and liabilities — whether taxes are missing from vendor invoices or need to be accrued. But what if tax is included? Is it accurate? Appropriate for the transaction? And are the processes behind it sound enough to avoid exposure? 

This is where the strategic power of reverse audits comes into play. 

Often seen as reactive, reverse audits are typically considered only after an audit notification arrives or the audit occurs. But in today’s environment (where audit activity is rising and virtual reviews are common), they deserve a proactive place in your compliance strategy. 

By reviewing past transactions, reverse audits help identify overpaid taxes, uncover refund opportunities, correct misclassifications and strengthen your compliance posture. They also reveal systemic issues that, if left unchecked, could lead to future risks. 

Reverse audits also boost compliance confidence. By resolving discrepancies early, tax teams align systems with current regulations, reducing penalties and improving governance. They create opportunities to engage departments like procurement, finance and IT – elevating tax from a reactive role to a strategic partner. 

With audit activity back to pre-pandemic levels and virtual audits on the rise, being audit-ready is essential. Reverse audits help teams stay ahead, identifying issues before they become liabilities. 

Common Issues Reverse Audits Can Uncover

Here are some of the most frequent problems reverse audits bring to light— issues that, if left unaddressed, can snowball into costly exposures: 

• Incorrect tax coding: Items may be misclassified in ERP or tax systems, leading to overpayment or underpayment of tax. 

• Overcollection of tax: Vendors may charge tax on exempt items or services due to misunderstanding jurisdictional rules. 

• Missed exemptions: Failure to supply valid exemption certificates can result in unnecessary tax payments. 

• Duplicate payments: Tax may be paid twice (once to the vendor and again through self-accrual) due to lack of coordination. 

• Inconsistent application of tax rules: Different departments may interpret taxability differently, especially in decentralized organizations. 

• Outdated tax rates or rules: Systems not updated with current rates or jurisdictional changes can lead to errors. 

• Lack of documentation: Missing or incomplete records can prevent recovery of overpaid tax and weaken audit defense. 

• Vendor errors: Suppliers may apply incorrect tax rates or jurisdictions, especially in multi-state or multi-country transactions. 

• Missed inclusion of tax refunds: When sales tax has been refunded to customers or bad debts are recognized on taxable sales, failure to include these deductions on sales tax collected result in refunded tax to customers without receiving the refund from the state. 

Identifying these issues early allows tax teams to correct course, recover funds, and prevent future occurrences. It also sets the stage for a more proactive approach to compliance. 

Reverse audits are more than a financial recovery tool—they’re a strategic lens through which tax teams can evaluate and improve their operations. They offer a chance to revisit assumptions, validate processes, and build stronger cross-functional relationships. 

For example, engaging with procurement can help ensure tax considerations are built into vendor onboarding and contract review. Partnering with IT can improve system configurations and data accuracy. Collaborating with finance can streamline reporting and reconciliation. These connections not only improve compliance, but they also enhance the tax department’s visibility and influence across the organization. 

Reverse audits also serve as a training opportunity. By analyzing past errors, tax teams can educate stakeholders on proper procedures, clarify taxability rules, and reinforce the importance of documentation. This knowledge-sharing helps build a culture of compliance and reduces reliance on reactive fixes. 

In today’s landscape, where tax complexity is growing and audit scrutiny is intensifying, reverse audits offer a way to stay ahead. They help organizations anticipate challenges, respond with confidence, and continuously improve. 

As I’ve shared in previous Vertex blogs, shifting from reactive to proactive is key. Reverse audits embody that shift — not just by recovering money, but by enabling a more agile, informed tax function.