Selling in the United States is one of the most effective ways to scale your e-commerce or digital business. But as you grow, the complexity of the US tax landscape grows with you. If you are an international seller, a SaaS provider, or a fast-growing SME, you’ve likely heard the term "nexus" tossed around.
In 2026, the rules are sharper, the thresholds are tighter, and the IRS and state authorities are more vigilant than ever. Many businesses unknowingly leave themselves exposed to massive back-tax liabilities and penalties simply because they are operating on outdated information.
Don't worry, getting compliant doesn't have to be a nightmare. Here are the seven most common mistakes businesses make with USA Sales Tax Nexus and exactly how you can fix them today.
1. Believing You Only Need a Physical Office to Trigger Nexus
This is the "old school" rule that still trips up even seasoned entrepreneurs. For decades, you only had to worry about sales tax if you had an office, a storefront, or employees in a state. That changed forever with the South Dakota v. Wayfair decision.
Today, Economic Nexus is the primary driver for tax obligations. If your sales exceed a certain dollar amount (often $100,000) or a specific number of transactions in a state, you have nexus. It doesn't matter if you’ve never stepped foot in that state.
How to fix it:
Stop looking for offices and start looking at your data. You need to perform a nexus study across all 50 states. Many states have recently adjusted their thresholds for 2026. For a deeper look at what has changed this year, check out our guide on why everyone is talking about 2026 US tax updates.
2. Overlooking Inventory Stored in Third-Party Warehouses (FBA)
If you use Amazon FBA, Walmart Fulfillment, or any third-party logistics (3PL) provider, your inventory is likely scattered across multiple states. Even if you don't have economic nexus based on sales volume, physical nexus is triggered the moment your goods sit on a shelf in a warehouse.
International sellers often miss this because they don't choose where Amazon sends their stock. However, most states view stored inventory as a "physical presence." If your product is in a California warehouse, you likely have a filing obligation in California.
How to fix it:
Download your inventory placement reports. You need to identify every state where your goods are stored and register for sales tax permits in those jurisdictions. Doing this manually is a chore, which is why our Global Tax Compliance Suite monitors these movements for you daily.
3. Relying Entirely on Marketplace Facilitator Laws
It is a common misconception that because Amazon or eBay collects and remits tax on your behalf, you are "off the hook." While Marketplace Facilitator (MPF) laws have simplified things, they aren't a total shield.
First, some states still require you to file "zero-tax" returns even if the marketplace collected everything. Second, if you sell through your own website (like Shopify) in addition to a marketplace, those sales must be aggregated to see if you hit nexus thresholds. If you hit nexus via Amazon, you are now responsible for collecting tax on your Shopify sales in that state too.
How to fix it:
Don't assume the platform handles 100% of your compliance. You must maintain independent sales records. We recommend reading our 5 things international sellers must know today to understand the gaps in marketplace coverage.
4. Miscalculating the 2026 Threshold Changes
State laws are not static. In late 2025 and moving into 2026, several states have moved to eliminate the "200 transaction" count and focus solely on revenue thresholds to simplify rules for small businesses. However, other states have lowered their revenue thresholds to capture more tax from digital services and SaaS.
If you are basing your compliance on 2023 or 2024 data, you are likely already out of compliance. Furthermore, the new reporting rules for 1099-K forms mean the IRS has more visibility into your high-volume sales than ever before.
How to fix it:
Monitor your gross sales and transaction counts monthly. To stay ahead of the game, you should review the new $5,000 1099-K reporting rule which significantly impacts how your income is reported to authorities.
5. Registering for a Tax Permit Too Late (or Too Early)
Timing is everything. If you register for a sales tax permit after you’ve already crossed the nexus threshold, you may be liable for back taxes and penalties for the period you were active but unregistered. Conversely, registering too early in states where you have no sales creates an unnecessary administrative burden of filing monthly "zero" returns.
How to fix it:
The moment you see your sales trending toward a state's threshold (usually at the 80% mark), begin the registration process. This gives you enough lead time to have your permit ready by the time you officially cross the line.
6. Ignoring "Click-Through" and Affiliate Nexus
Do you have influencers in Florida promoting your products? Or affiliates in New York? Many states have "Click-Through Nexus" or "Affiliate Nexus" laws. This means if an in-state resident refers customers to your site in exchange for a commission, and those sales exceed a certain amount, you have established nexus.
This is a major trap for modern digital brands that rely heavily on social media marketing. You might think you're just paying for ads, but the state sees a business relationship that triggers tax collection.
How to fix it:
Audit your affiliate and influencer list by state. If you have significant sales coming from specific regions via affiliates, check those states' specific nexus definitions regarding "remote solicitors."
7. Failing to Manage Exemption Certificates Correctly
If you sell B2B or to wholesalers, you might not have to collect sales tax, if you have a valid exemption certificate from the buyer. A major mistake businesses make is failing to collect these certificates or letting them expire. During an audit, if you can’t produce a valid certificate for a tax-exempt sale, the state will demand the tax (plus interest) from your pocket.
How to fix it:
Implement a digital system to collect and store exemption certificates at the point of sale. Treat these documents like gold; they are your only defense in a B2B sales tax audit.
Moving Toward Total Compliance in 2026
The US sales tax system is designed to be automated, but it requires accurate data and constant oversight. Trying to manage this yourself as an international seller often leads to expensive errors.
At Sterlinx Global, we don't just "advise", we execute. We provide a full-suite accounting and compliance service where you provide the data, and we handle the bookkeeping, tax calculations, and filings on your behalf. Whether you are dealing with US LLCs, UK Limited Companies, or any international entity, our goal is to keep you compliant so you can focus on growth.
Are you unsure if you've triggered nexus in a new state?
Contact us today to speak with an expert and ensure your 2026 filings are bulletproof.
Frequently Asked Questions
What happens if I ignored sales tax nexus for the last two years?
You may be liable for back taxes, interest, and penalties. However, many states offer Voluntary Disclosure Agreements (VDA). This allows you to come forward, pay the back taxes, and often have the penalties waived. It is much better to come forward voluntarily than to wait for an audit.
Does every US state have sales tax?
No. There are five states, Alaska, Delaware, Montana, New Hampshire, and Oregon, that do not have a general state-level sales tax. These are often referred to as the "NOMAD" states. However, beware of local or municipal taxes in some of these areas.
How often do I need to file sales tax returns?
Filing frequency depends on your sales volume in each specific state. It can be monthly, quarterly, or annually. The state will typically assign your filing frequency when you register for your permit.
Is digital software (SaaS) subject to sales tax nexus?
In many states, yes. The definition of "tangible personal property" has expanded in many jurisdictions to include software-as-a-service and digital downloads. You must check each state's specific rules regarding digital goods.
Can Sterlinx Global handle my US Sales Tax if I am based in the UK or EU?
Absolutely. We specialize in cross-border compliance for international sellers. We manage everything from your initial nexus registration to the ongoing monthly filings, ensuring you never miss a deadline.
