The biggest sales tax mistake ecommerce businesses make is assuming they only need to collect sales tax in their home state. As online sales grow, businesses often trigger sales tax nexus in multiple states without realising it, leading to years of unpaid sales tax, penalties, and interest. This usually happens gradually.
A business:
- Starts selling online
- Expands nationally
- Uses Amazon FBA or Shopify
- Experiences rapid growth
But never updates its sales tax compliance strategy.
The result is hidden multi-state sales tax exposure.
By the time many ecommerce businesses realise there is a problem they may already owe years of uncollected sales tax.
The most important point to note is that ecommerce businesses can owe thousands in unpaid sales tax if they accidentally trigger nexus in multiple states and fail to register or collect tax correctly.
Why This Sales Tax Mistake Happens So Often
Most ecommerce businesses do not intentionally ignore sales tax obligations. Instead sales tax complexity grows faster than the business expects.
This is especially common for:
- Shopify sellers
- Amazon FBA businesses
- Multi-channel ecommerce brands
- International sellers entering the US market
Many businesses simply do not realise how quickly nexus obligations appear.
Why Sales Tax Problems Grow Silently
Sales tax exposure often builds quietly in the background.
Businesses focus on:
- Revenue growth
- Advertising
- Inventory management
- Scaling operations
Meanwhile state sales tax obligations continue increasing automatically.
This is why many businesses only discover the issue after:
- Receiving a state notice
- Applying for investment
- Selling the business
- Undergoing due diligence
- Being audited
The Hidden Nexus Triggers Ecommerce Businesses Miss
1. Economic Nexus Thresholds
Economic nexus is one of the biggest hidden ecommerce sales tax risks.
Most states require businesses to register once sales exceed thresholds such as:
$100,000 in revenue
$500,000 in larger states
200 transactions
The problem is many businesses exceed thresholds without tracking sales by state.
2. Amazon FBA Inventory Creates Physical Nexus
Amazon FBA frequently creates hidden physical nexus across multiple states.
Amazon may store inventory in:
- Texas
- California
- Florida
- Illinois
- Other warehouse states
Even if the seller:
- Never chose those states
- Has no office there
- Has no employees there
The stored inventory may still create immediate sales tax obligations.
3. Combined Marketplace Sales Push Businesses Over Thresholds
Many ecommerce brands sell through:
- Shopify
- Amazon
- Etsy
- Walmart Marketplace
States often combine all sales into the state when calculating thresholds.
4. Shopify Tax Settings Are Misconfigured
Incorrect Shopify sales tax settings are one of the most common ecommerce compliance problems.
Common issues include:
- Wrong states activated
- Shipping not taxed correctly
- Product taxability errors
- Failure to update settings after crossing thresholds
Businesses often assume if Shopify isn’t charging tax, everything must be configured correctly. Unfortunately Shopify only calculates based on the settings you provide.
Why Ecommerce Businesses Often Don’t Discover the Problem Early
Marketplace Facilitator Confusion
Marketplace facilitator laws require marketplace facilitators, like Amazon, and some platforms to collect sales tax on behalf of sellers
This creates false confidence because businesses assume “Amazon handles everything.”
However:
- Marketplace sales may still count toward nexus thresholds
- Registration obligations may still exist
- Filing requirements may still apply.
International Seller Misunderstanding
Many overseas ecommerce businesses believe US sales tax only applies to US companies, which is incorrect. Economic nexus laws now apply to international ecommerce sellers too.
How States Detect Ecommerce Businesses
States are significantly better at identifying ecommerce sellers than many businesses realise.
Modern enforcement increasingly relies on:
- Marketplace reporting
- 1099-K payment processor data
- Shopify transaction information
- AI-driven compliance systems
States can now identify the below far more efficiently than before:
- unregistered businesses
- threshold breaches
- missing filings
- nexus exposure
What Happens If the Problem Is Ignored?
Ignoring sales tax nexus exposure can become extremely expensive.
States may assess:
- Back taxes
- Interest
- Penalties
The biggest issue is businesses often cannot recover the missing tax from past customers later. This means the business may need to pay the liability itself.
Why This Can Cost Businesses Thousands
Sales tax exposure compounds quickly because:
- Multiple states may be involved
- Exposure can go back several years
- Penalties and interest continue growing
For fast-growing ecommerce brands, liabilities can escalate surprisingly quickly.
How Ecommerce Businesses Can Fix Sales Tax Problems
Step 1: Conduct a Nexus Review
Review:
- Sales by state
- Inventory locations
- Marketplace activity
- Fulfilment operations
Step 2: Identify Historical Exposure
Determine:
- When nexus began
- Which states may have exposure
Step 3: Avoid Panic Registration
Immediately registering without strategy can:
- Increase historical exposure
- Complicate voluntary disclosure opportunities.
Step 4: Explore Voluntary Disclosure Agreements (VDAs)
In many cases:
- VDAs may reduce penalties
- Limit lookback periods
- Create structured compliance pathways
Worked Examples
Example 1: Shopify Seller
- Exceeds nexus thresholds in multiple states
- Continues collecting tax only in home state
Result:
Multi-state historical exposure builds quietly.
Example 2: Amazon FBA Seller
- Inventory stored nationwide through Amazon warehouses
Result:
Physical nexus triggered in several states without the seller realising.
Example 3: International Ecommerce Brand
- UK business scales rapidly into the US market
- No sales tax registrations in place
Result:
Significant multi-state nexus exposure discovered during compliance review.
Common Sales Tax Mistakes Ecommerce Businesses Make
- Assuming sales tax only applies in the home state
- Ignoring economic nexus thresholds
- Forgetting Amazon inventory creates nexus
- Assuming Shopify handles compliance automatically
- Waiting until states issue notices or audits
These mistakes often create years of unnoticed liability.
FAQs
What is the biggest sales tax mistake ecommerce businesses make?
Failing to recognise when multi-state nexus obligations have been triggered.
Can ecommerce businesses owe sales tax they never collected?
Yes, states may still assess the liability against the business.
Does Amazon FBA create sales tax nexus?
Often yes, because inventory storage creates physical nexus.
Can Shopify sales trigger nexus?
Yes, Shopify sales commonly contribute toward economic nexus thresholds.
What happens if I ignored sales tax obligations for years?
You may have historical exposure, but voluntary disclosure options may help reduce penalties and liability.
Final Thoughts
As ecommerce businesses scale nationally and internationally, sales tax obligations often become far more complex than owners expect.
The key takeaway is that the most expensive sales tax mistake is not realising your business created nexus in multiple states until years of liability have already accumulated.
By proactively monitoring sales tax exposure, ecommerce businesses can:
- Reduce financial risk
- Avoid audit problems
- Protect profitability as they grow
If you think your ecommerce business may have hidden sales tax exposure, RJM Tax Exemption can help assess your nexus risk, identify historical liabilities, and guide you through the best strategy for becoming compliant.
