Marketplace facilitator sales tax: who collects and what you still owe

States define a marketplace facilitator broadly as a business that runs a platform where third parties sell and that processes payment for those sales. After South Dakota v. Wayfair, states with a sales tax adopted laws requiring these platforms to collect tax on facilitated sales once they meet the state's threshold. Definitions and thresholds vary by state.

When a facilitator collects, it's generally responsible for the tax on those sales, and the seller doesn't report them as taxable sales — though some states still require the seller to report them as exempt or deductible on its own return. Keep marketplace reports showing tax collected; they're your proof in an audit.

• Your own website sales. A Shopify or WooCommerce store isn't a facilitator for your sales — you collect where you have nexus.
• Wholesale and in-person sales. Trade shows, pop-ups and B2B orders are your responsibility.
• Threshold counting. Some states count marketplace sales toward your economic nexus threshold, so high marketplace volume can require you to register for your direct sales even if they're small.

Sellers often assume being on a marketplace means they never need to register anywhere, or they charge tax on their own site only in their home state. Inventory stored by a fulfillment program can also create physical nexus in states where you never sold directly. Check your exposure with the multistate nexus checker.

If you've had direct sales into states where you had nexus, a voluntary disclosure can usually resolve it with limited lookback. The Streamlined Sales Tax program offers one registration for member states. See the e-commerce tax guide or take the free business tax relief assessment.