What it is

A Certified Service Provider (CSP) is “an agent certified under the Streamlined Sales and Use Tax Agreement to perform all the seller’s sales and use tax functions, other than the seller’s obligation to remit tax on its own purchases.” <!– src: https://www.streamlinedsalestax.org/certified-service-providers/what-is-a-csp –> In plain terms, it is a software company whose tax engine has been tested and certified by Streamlined Sales Tax (SST) member states for accuracy, and which you can hire to run your sales tax compliance from start to finish.

A CSP typically handles the full lifecycle: identifying taxable products, applying the correct state and local rates, maintaining records, integrating with your commerce system, preparing and filing returns, remitting tax to member states, and responding to notices and audits. <!– src: https://www.streamlinedsalestax.org/certified-service-providers/what-is-a-csp –> The seller’s main remaining job is to send the data and pay any tax on its own purchases. As of 2026 there are five certified CSPs: Avalara, TaxCloud, Sovos, AccurateTax, and Avior.

Why it matters to a multi-state seller

For a seller filing across many states, the CSP model is attractive for one headline reason: in SST member states it can be free. The states compensate CSPs directly for handling sellers who meet the “CSP-compensated seller” definition — generally remote sellers that have economic nexus in the state but no physical presence there. <!– src: https://www.streamlinedsalestax.org/for-businesses/remote-seller-faqs/lists/csp-faqs-for-sellers/what-is-a-volunteer-seller-for-purposes-of-csp-compensation –> A CSP-compensated seller is not charged a filing fee, because the member state pays the provider.

That turns what is normally a recurring software-and-filing cost into a state-funded service for the member-state portion of your footprint. It also reduces audit risk: because the software is state-certified, sellers using it in good faith generally receive liability relief for errors caused by the certified system.

But the benefit has hard edges. CSP compensation applies only in SST member states, and only for sellers who meet the compensated-seller definition. Large non-member markets — California, Texas, Florida, New York — sit outside the program, so a CSP either charges you for those states or doesn’t cover them. The “free” headline is real but partial.

Worked example

Suppose you are a remote e-commerce seller with economic nexus in five SST member states and three non-member states.

• In the five SST member states, you contract with a CSP. Because you are a remote seller meeting those states’ economic nexus standards and have no physical presence there, you qualify as a CSP-compensated seller. The states pay the CSP, and you pay no filing fee for those states — the provider calculates tax, files the simplified returns, and remits on your behalf. <!– src: https://www.streamlinedsalestax.org/for-businesses/remote-seller-faqs/lists/csp-faqs-for-sellers/what-is-a-volunteer-seller-for-purposes-of-csp-compensation –>
• In the three non-member states, the CSP-compensation arrangement doesn’t apply. You either pay the provider’s standard fees to file there or arrange filing another way.

The result: five states’ worth of calculation, filing, and remittance handled at no cost, and three states handled on a paid or separate basis. Your job shrinks to feeding accurate sales data and paying use tax on your own purchases.

State-level nuance

Whether a CSP is free turns entirely on state membership and seller type, so the program is genuinely state-variable:

The “CSP-compensated seller” definition is used only to determine when a CSP gets paid by a state — it does not change your legal duty to register and remit wherever you have nexus. <!– src: https://www.streamlinedsalestax.org/Shared-Pages/faqs/FAQs—about-certified-service-providers –> Because membership and the certified-provider roster can change, confirm both with the SST Governing Board before relying on free service in any given state.

How this connects to staying compliant

A CSP is an execution layer, not a substitute for knowing where you owe tax. You still need a nexus determination to know which states you must register in, and the SST registration system to enroll in member states. The CSP then takes over the mechanical work — rates, returns, remittance — in the member states it covers. The gap a CSP leaves is the non-member states and any state where you have physical presence, which is exactly where a multi-state seller most needs a coordinated plan rather than a single piece of software.

Sources: Streamlined Sales Tax — What is a CSP: https://www.streamlinedsalestax.org/certified-service-providers/what-is-a-csp Streamlined Sales Tax — FAQs about Certified Service Providers: https://www.streamlinedsalestax.org/Shared-Pages/faqs/FAQs—about-certified-service-providers Streamlined Sales Tax — CSP-compensated seller FAQ: https://www.streamlinedsalestax.org/for-businesses/remote-seller-faqs/lists/csp-faqs-for-sellers/what-is-a-volunteer-seller-for-purposes-of-csp-compensation Streamlined Sales Tax — Certified Service Providers (about): https://www.streamlinedsalestax.org/certified-service-providers/certified-service-providers-about