Who holds audit liability in SST states — me or my CSP?

The SST program provides meaningful protection to enrolled sellers when their CSP makes an error. In SST states, if your CSP miscalculates tax or files incorrectly and that error results in underpayment, you are generally protected from the resulting penalties and interest: the liability for the CSP-caused mistake shifts to the CSP’s account with the state.

This is one of the less-publicized benefits of CSP enrollment, and it’s genuinely valuable.

How the protection works

The SST Agreement includes a seller protection provision. Under this provision:

When a seller is properly enrolled in the SST program through a CSP, and the CSP makes a calculation or filing error that results in an underpayment to a member state, the seller is not assessed penalties or interest for that underpayment. The CSP is responsible for the error.

The underlying tax may still be owed: the state can collect the correctly-calculated tax for the period, but the penalties and interest arising from the CSP’s mistake are not assessed against the seller.

What this means in practice

Errors in sales tax calculation happen. Rate changes, local surtax updates, product taxability questions, even well-run compliance operations have periods where the math is slightly off. In a non-SST state, or with a non-CSP provider, that error falls entirely on the seller: back tax owed, penalties, and interest.

In SST states through a CSP, the seller’s exposure for a CSP-caused error is limited to the corrected tax itself. The penalty and interest component, which can be 15–25% of the underpayment plus monthly interest, is not your problem when the CSP caused the mistake.

For sellers filing in 10+ SST states monthly over several years, this protection has real value. The probability of at least one period having a rate or taxability error compounds over time. Seller protection converts what would be a penalty event into a correction.

What the protection doesn’t cover

Seller protection is conditional. It does not apply when:

The seller provided inaccurate information. If you gave your CSP incorrect data, misclassified products, wrong exemption status, incomplete nexus information, and that caused the underpayment, the error originated with you, not the CSP. Protection doesn’t apply.

The seller committed fraud. Intentional underreporting, falsified records, or deliberate evasion void the protection entirely and expose the seller to the full range of penalties including criminal liability in serious cases.

The seller wasn’t properly enrolled. Seller protection applies only to sellers who have gone through the formal SST enrollment process through a certified CSP. Sellers who are registered but not formally enrolled, or who used a non-CSP provider, are not protected.

Non-SST states. This protection exists only within the SST program framework. In California, Texas, New York, Florida, and the other non-SST states, standard liability rules apply regardless of who filed the return.

What an audit looks like in an SST state

Being enrolled in SST through a CSP does not make you immune to audits. A state can still examine your sales records, review your product classifications, and verify your nexus analysis. The audit process in SST states is similar to other states.

What changes is the consequence of findings. If an audit uncovers errors in an SST state that were caused by your CSP’s calculation engine, seller protection limits your exposure to the corrected tax, not the full tax plus penalties plus compounded interest.

If the audit finds errors caused by information you provided, product codes you assigned, exemption certificates you didn’t collect, nexus you failed to disclose, those fall on you regardless of the SST program.

The comparison to non-SST states

In non-SST states, there is no equivalent seller protection mechanism. If your provider files incorrectly in California or Texas and an audit catches the error, you owe the corrected tax plus all applicable penalties and interest. Your remedy is against your provider (potentially), but the state’s claim is against you.

This asymmetry is another dimension of the SST benefit that’s underappreciated. The free-filing benefit is visible and quantifiable. The audit protection is less visible but meaningful over a multi-year compliance horizon.