What are the sales tax collection responsibilities for online marketplaces?

Overview

Online marketplaces can have a legal obligation to collect, remit, and report sales tax for transactions that occur on their platform. States assign those duties through a mix of economic‑nexus thresholds and marketplace‑facilitator laws; the result is that sometimes the marketplace collects tax on behalf of third‑party sellers, and sometimes the seller is responsible. Failing to recognize which party must collect sales tax can lead to audits, penalties, and liability for back taxes.

Background and legal turning point

The U.S. Supreme Court decision in South Dakota v. Wayfair, Inc. (2018) allowed states to require remote sellers to collect sales tax based on economic presence rather than physical presence. Since then, most states have adopted economic‑nexus thresholds and explicit marketplace‑facilitator rules that shift collection and remittance duties to platforms in many common scenarios (see National Conference of State Legislatures guidance: https://www.ncsl.org/research/fiscal-policy/sales-tax-on-internet-sales.aspx).

How responsibilities are typically allocated

  • Marketplace‑facilitator laws: Many states require the marketplace (the platform) to collect and remit sales tax on sales made by third‑party sellers through the platform. See our explainer on marketplace facilitator rules for details: Marketplace Facilitator Rules: Who Collects and Remits Sales Tax?.
  • Economic nexus and seller obligations: Sellers that exceed state sales or transaction thresholds must register and collect tax in that state unless the marketplace does so on their behalf.
  • Nexus from inventory/fulfillment: If a marketplace or seller stores inventory in a state (for example, in an FBA warehouse), that storage can create nexus and trigger collection duties. For specifics when using fulfillment services, see: State Sales Tax Registration for Sellers Using Fulfillment by Amazon.

Practical examples

  • A large marketplace with national reach commonly collects and remits sales tax for most states that have facilitator rules. The platform reports and pays taxes for the sale, and third‑party sellers receive transaction reports showing tax collected.
  • A small seller on a marketplace may still need to register in a state and file returns if the marketplace does not collect tax for their sales, or if state law still places the final responsibility on sellers.

In my practice working with e‑commerce businesses, I frequently find the same pattern: marketplaces will collect tax in states with clear facilitator statutes, but sellers remain responsible for registration and filings in states where the marketplace does not collect or where seller‑level reporting is required.

Step‑by‑step compliance checklist

  1. Run a nexus assessment: Identify states where you (and your marketplace) have economic nexus, inventory, employees, or other nexus triggers.
  2. Confirm marketplace policies: Review the marketplace’s tax collection and reporting policies (who collects, how tax appears on seller reports, and whether the marketplace provides exemption handling).
  3. Register where required: If you must collect tax, register for a sales tax permit in each state where you have an obligation.
  4. Implement automation: Use tax engines or marketplace tools to calculate rate and taxability by jurisdiction — reduces errors (see our guide on automation tools: https://finhelp.io/glossary/sales-tax-compliance-automation-tools-for-small-e-commerce-businesses/).
  5. File and remit on schedule: Follow the state’s filing frequency and remit collected taxes on time.
  6. Keep records: Maintain transaction-level records, exemption certificates, and marketplace reports for audits.

Common mistakes to avoid

  • Assuming physical presence is the only trigger — economic nexus and facilitator laws matter.
  • Relying solely on marketplace statements without verifying whether the marketplace collects in every state where you have nexus.
  • Skipping registration because the marketplace collected tax historically — state laws and marketplace policies can change.

Frequently asked questions (short answers)

  • Who usually pays the tax burden: the buyer pays the tax at purchase; the marketplace or seller remits that tax to the state.
  • Can a marketplace shift liability back to sellers: Some contracts attempt to shift liabilities, but state collections laws and audit practices determine ultimate responsibility.

Authoritative sources and further reading

Professional disclaimer

This article is educational and not legal or tax advice. For obligations specific to your marketplace or business, consult a tax professional or state tax authority.

Internal resources

If you want a short checklist customized to your marketplace model (fulfillment‑based, dropship, or direct fulfillment), consult a CPA experienced in multistate sales tax.