Your E-Commerce Clients May Not Be as Compliant as They Think

Most e-commerce sellers believe sales tax is a solved problem. They picked a platform, switched on tax collection, and moved on. In the work I do helping firms untangle exposure, that confidence is almost always where the trouble starts.

The confidence that hides the risk

Here's a pattern I run into constantly. A brand runs most of its volume through a major marketplace that collects and remits on its behalf. They also keep a small direct storefront on the side, a few thousand dollars a month, nothing anyone thinks about. A state flags them as required to register anyway. Not because of the direct sales, which are tiny, but because that state counts the marketplace sales toward the economic nexus threshold even though the marketplace is the one remitting the tax.

The seller crossed the threshold on marketplace volume, and now they're on the hook to register and collect on their direct sales. The only way they'd avoid it is if 100% of their sales into that state ran through the marketplace. The moment a single direct order exists, the calculus flips.

That's the disconnect worth sitting with. Marketplace collection does not shield the seller. It protects the marketplace.

What marketplace collection actually covers

Marketplace facilitator laws require platforms like Amazon, Etsy, and Walmart Marketplace to collect and remit sales tax for sellers in most states. That's real, and it covers a meaningful slice of the obligation. But it only covers what happens on that one marketplace. The moment a client sells through their own Shopify store, takes a wholesale order, or lights up a second channel, they've stepped outside that protection, usually without noticing.

Nothing about the business changed in a way a bookkeeper would flag. There's no line item that says "you now owe tax you didn't owe last month." The obligation just quietly appears, and it usually gets discovered only when a state notice comes in.

Nexus creep is faster for e-commerce

Sales channels multiply faster for e-commerce clients than for almost any other business I work with, and each new channel is a potential blind spot:

• Adding a wholesale or B2B arm alongside direct-to-consumer sales
• Selling on a second or third channel with different collection rules
• Using a fulfillment network that creates physical nexus through inventory storage
• Running limited-time promotions or pop-up sales in new states
• Expanding across borders and triggering VAT or GST obligations alongside domestic sales tax

Any one of these can create a new obligation. Together they compound, and most firms don't have a standing process to catch them as they happen rather than a year later. I've seen a single brand add a short-video shopping channel, a marketplace, and a warehouse-club wholesale account in one year, each taxed and monitored differently, none of them announcing itself.

Product taxability adds another layer

E-commerce clients also hit taxability questions a typical local business never sees. Digital products, bundles of physical and digital goods, and subscriptions are taxed differently state by state, and sometimes differently within one state depending on how the item is delivered. A client selling a physical product bundled with a digital download might owe tax on the full bundle in one state and only the physical portion in another.

It gets harder as the catalog grows. A client who started with one physical product and later added a companion app or a subscription tier has created several new taxability questions. Firms that set taxability once at onboarding and never revisit it are exposed every time the product mix shifts. The classification that was right on day one rarely survives two years and three launches.

Your client's inventory can create nexus they can't see

The one that catches even experienced State and Local Tax (SALT) practitioners is physical nexus created through fulfillment. Clients using third-party logistics or a marketplace fulfillment program can establish physical presence in states they've never set foot in, because inventory sitting in a warehouse is enough to trigger a registration requirement in most states, regardless of sales volume.

I've watched it happen more than once: a seller required to register in a state purely because a fulfillment network parked its inventory in a warehouse there. No sales threshold, no employees, no say in where the inventory landed.

For a nexus review, that means physical presence can't be assessed by asking where the client has an office or staff. It also requires asking where their inventory actually sits, which is often a conversation the client has never had to have.

What this means for your firm

The clients most at risk aren't careless. They're confident, because a marketplace is collecting it or because nothing has "changed" in their eyes. That is exactly why this belongs in a proactive review, not a reaction to a notice. A few questions worth asking any e-commerce client:

• Which platforms and channels are you selling through, and has that changed in the last year?
• Are you assuming marketplace collection covers everything, or have you confirmed which channels it actually applies to?
• Have you added fulfillment centers, warehouses, or drop-shipping that could create physical nexus?
• Has your product mix shifted in a way that could change how it's taxed?
• Have you started selling internationally, and if so, are VAT or GST obligations being handled separately from U.S. sales tax?

A fast way to answer the nexus question concretely is a full exposure check, a nexus study that maps a business's sales tax, VAT, and GST exposure across every channel, rather than trusting assumptions. Firms that ask these questions early catch exposure while it's still cheap to fix. Firms that wait, find out during an audit, when the fix costs far more than the review would have, and the client is far less forgiving of a gap nobody flagged.

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