What it is

Marketplace nexus is the sales tax obligation that arises when you sell through a marketplace facilitator — a platform like Amazon, Etsy, Walmart, or eBay that lists products, processes payments, and handles checkout for third-party sellers. Under marketplace facilitator laws, the responsibility for collecting and remitting sales tax on those transactions shifts from the individual seller to the platform.

These laws emerged right after the South Dakota v. Wayfair, Inc. decision in 2018 opened the door to taxing remote sales. Washington’s law took effect January 1, 2018, and within a few years every U.S. state with a sales tax (plus D.C.) had enacted one. The platform registers, collects the correct tax from buyers at checkout, and remits it to the state on the seller’s behalf, generally once the facilitator’s total sales into the state cross that state’s economic nexus threshold.

The key nuance — and where sellers get caught — is that marketplace facilitator laws cover only the sales made through that marketplace. They do not erase your obligations on sales you make through other channels, and in most states the marketplace sales still count toward your own economic nexus threshold.

Why it matters to a multi-state seller

If you sell exclusively through one marketplace and it collects in every state, your day-to-day collection burden is light — the platform handles it. But two things keep marketplace nexus on your radar.

First, mixed channels. The moment you also sell direct — through your own Shopify store, wholesale, or another channel where no facilitator collects — you are responsible for the tax on those sales wherever you have nexus. The marketplace doesn’t help you there.

Second, threshold math. Most states require you to include your marketplace sales when measuring whether you’ve crossed their economic nexus threshold, even though the platform is the one collecting on them. So your Amazon volume can push your direct-sales channel over the line and force you to register, even if Amazon is already collecting on the marketplace side.

Worked example

Say you sell on Amazon (a marketplace facilitator) and also run your own Shopify store. In one state with a $100,000 threshold that counts marketplace sales toward it:

• Amazon sales into the state: $73,000 → Amazon collects and remits the tax on these.
• Direct Shopify sales into the state: $52,000 → no facilitator collects; this is on you.
• Combined for threshold: $73,000 + $52,000 = $125,000 → over the $100,000 threshold → you have economic nexus.

Result: you must register and collect on the $52,000 of direct sales. Amazon keeps handling its $73,000, but the marketplace volume is what pushed your total over the line. (This $73,000 + $52,000 = $125,000 illustration follows the Idaho example documented by the Sales Tax Institute.)

State-level nuance

The pattern is consistent — every sales-tax state makes the facilitator collect — but two details vary:

• Do marketplace sales count toward your own threshold? Most states say yes, but some let you exclude facilitator-collected sales, which can keep a marketplace-only seller under the threshold.
• **Do you still have to register if you sell only through marketplaces?** Some states say no — a 100%-marketplace seller need not register or file even above the threshold. Others (for example, Connecticut) require registration but provide a simplified filing where you check a “marketplace seller” box and deduct the facilitator-collected sales.

Because both the threshold-counting rule and the registration rule are state-specific, a seller with the same sales can have very different filing duties from one state to the next.

How this connects to staying compliant

Marketplace facilitator laws simplify collection but don’t eliminate compliance. The questions you still have to answer are: where do my combined sales (marketplace plus direct) create nexus, where do I have direct sales that no platform is collecting on, and which states require me to register even for marketplace-only activity? Where you sell direct into a nexus state, you must register, collect, and file yourself — sometimes filing a “zero return” that reports total sales but deducts the facilitator-collected portion so you aren’t taxed twice.

The discipline is the same as for any nexus: track sales by state and channel, know which platform is collecting where, and register where your own obligations remain.

Sources: TaxJar — Marketplace facilitator laws, explained: https://www.taxjar.com/sales-tax/marketplace-facilitator-laws Sales Tax Institute — What marketplace sellers need to know about sales tax nexus: https://www.salestaxinstitute.com/resources/what-marketplace-sellers-need-to-know-about-sales-tax-nexus Avalara — State-by-state guide to marketplace facilitator laws: https://www.avalara.com/us/en/learn/guides/state-by-state-guide-to-marketplace-facilitator-laws.html South Dakota v. Wayfair, Inc., 138 S. Ct. 2080 (2018): https://www.supremecourt.gov/opinions/17pdf/17-494_j4el.pdf