One of our clients recently shared something with us. We asked if we could pass it along, because a lot of eCommerce sellers will recognize themselves in this story.
"I started my first Amazon business in 2019. I wanted to save every dollar I could. So when tax time came, I bought tax software and did it myself.
For five years, I thought I was being smart. I thought I was saving money. My business was growing. The IRS accepted my tax returns.
Then in year five, I got a letter from the IRS. They wanted to review my taxes. They found years of mistakes I didn't know I was making. When everything was resolved, I owed $47,000 — back taxes, late fees, and the cost to fix everything.
Yes, forty-seven thousand dollars."
This story is why we put this guide together. If you sell on Amazon, run a Shopify store, or have any online business, this is worth your time. These are the tax situations that catch eCommerce sellers every year — and understanding them is the first step to getting ahead of them.
Why eCommerce Taxes Have More Moving Parts
Traditional retail keeps things relatively simple. Buy products, sell locally, pay taxes in one place. eCommerce adds a lot of layers. You may have tax obligations in multiple states at once — and most sellers don't realize that until later.
The Multi-State Reality
Before 2018, sales tax only applied where you had a physical presence — a store, office, or warehouse. Then a major Supreme Court decision changed that. Today, the majority of states can require you to collect sales tax simply because you sell a certain volume there, regardless of where your business is located.
Each state sets its own rules. Most use $100,000 in sales or 200 transactions as the threshold. Some states differ — California and Texas set the bar at $500,000. New York requires both $500,000 in sales and at least 100 orders.
*Note: These thresholds reflect state rules as of tax year 2025. State economic nexus laws are updated regularly — if you're reading this in a later year, it's worth confirming current thresholds directly with each state or your tax advisor.
One thing that surprises many FBA sellers: Amazon stores inventory in fulfillment centers across the country. That means you may have a tax obligation in states where your products are sitting — even if you've never been there. Our client had unknowingly crossed the threshold in 23 states.
How Your 1099-K Works
Payment platforms like PayPal and Stripe are required to report your earnings to the IRS using a form called a 1099-K. Following the passage of the One Big Beautiful Bill Act (OBBBA), the federal reporting threshold has been permanently set to $20,000 in payments AND more than 200 transactions per platform, per year. Keep in mind: thresholds are measured per platform, not combined across apps — and all income remains taxable regardless of whether you receive this form.
State rules vary. Vermont, Maryland, Virginia, and Massachusetts use a $600 threshold, while Illinois and New Jersey set theirs at $1,000. If you're based in one of these states, your platform may issue a 1099-K well before you hit the federal threshold.
One thing worth understanding about the 1099-K: it reports gross receipts. It doesn't subtract fees or refunds. So if your payment platform reports $175,000 but your tax return shows $141,000, having clear documentation that explains that difference is what keeps your return clean and straightforward.
Five Things That Led to a $47,000 Bill
Looking back, we helped our client identify five key areas. Each one is more common than you'd think — and each one is avoidable.
#1: Miscalculating Cost of Goods Sold (COGS)
When you sell products, you can deduct what you paid for them. This is called Cost of Goods Sold, or COGS. The concept is simple. The details take a little getting used to.
COGS includes what you pay your supplier and the shipping cost to receive that inventory. It does not include Amazon fees or payment processing fees — those go in a separate expense category.
Two things that often get mixed up: counting product costs when inventory is purchased instead of when it's sold, and grouping Amazon storage fees in with product costs. If you buy $10,000 of inventory in December but sell it in January, that cost belongs on next year's return. Knowing this distinction from the start saves a lot of cleanup later.
#2: Not Tracking Inventory Consistently
The IRS requires sellers to report ending inventory at the close of each year — and to use the same valuation method consistently. Estimating, or skipping this step, creates a mismatch between what you report and what actually happened.
If your ending inventory is overstated, you end up reporting more profit than you made — and paying taxes on the difference.
A simple habit that helps: pull your Amazon Inventory Report on January 1st each year. It's much easier to capture in the moment than to reconstruct it months later.
#3: Missing Quarterly Estimated Tax Payments
If you expect to owe more than $1,000 in taxes for the year, the IRS requires payments throughout the year — not just at filing time. The due dates are April 15, June 15, September 15, and January 15.
This is a rule that's easy to know about and still miss in practice. Underpayment penalties apply even if you pay your full balance by April 15. In our client's case, those penalties alone came to over $8,000.
A system that works well for many sellers: set aside 25–30% of every payment received into a dedicated savings account, then pay on the quarterly schedule. Once it's automatic, it's one less thing to think about.
#4: Mixing Personal and Business Expenses
When personal and business spending share the same account or card, every transaction needs to be explained during a review. What starts as a routine process becomes a time-consuming one.
Our client spent three weeks going through individual charges — and lost some deductions they were entitled to simply because they couldn't clearly document the business purpose. Keeping accounts separate from the beginning is one of the most straightforward protections you can give yourself.
#5: Placing Deductions in the Wrong Categories
Where a deduction is placed on your return affects how much tax benefit you actually receive. Some categories reduce self-employment tax. Others only reduce income tax. The difference adds up over time.
Property taxes on a business building, for example, can be placed in different spots depending on your return structure. Knowing the options — and using the right one — is something that's easy to miss when you're filling in boxes without the full picture.
How the IRS Reviews Returns
The IRS audits less than 1% of tax returns, and their selection process is data-driven. Automated systems compare numbers across sources. If your payment platform reports $175,000 in receipts and your return shows $141,000, that gap gets flagged for a closer look. Deductions that are significantly higher than similar businesses in your category can attract attention, as can consistent losses across multiple years.
Tax software helps you fill in the correct fields. A knowledgeable tax professional helps you understand why your numbers look the way they do — and how to present them clearly and accurately.
The Real Math of DIY vs. Professional Help
Here's the comparison our client ran after the fact.
Tax software: roughly $150–250 per year. Over five years: about $1,000.
An eCommerce tax professional: roughly $800–2,500 per year. Over five years: about $4,000–12,500.
The five-year DIY "savings": somewhere between $3,000 and $11,000.
The actual cost: $47,000 in back taxes, penalties, and resolution fees. Plus $6,200 in missed deductions. Plus roughly 200 hours of time spent during the audit. Plus business momentum lost while managing the process.
Professional support would have paid for itself several times over.
What eCommerce Sellers Need to Stay Organized
If you're currently managing your taxes independently, here's what needs to stay current:
Federal tax return
State tax return where your business is based
Sales tax filings in every state where you've met the threshold (for FBA sellers, this can mean 40+ states)
Quarterly estimated tax payments — four times per year
Accurate, consistent records of inventory and product costs
Documentation to reconcile your 1099-K forms with what you report
Clear records showing each business expense was business-related
For FBA sellers, multi-state sales tax is where complexity grows quickly. Each state has its own filing deadlines, and missing a filing — even when you owe nothing — can result in penalties.
Tools that connect your sales platforms to your books help a lot here. At Tall Oak Advisors, we work with Link My Books and QuickBooks to keep eCommerce books accurate and current month to month — so nothing gets missed at filing time.
What to Look for in an eCommerce Tax Professional
Not every accountant works regularly with online sellers. When you're evaluating someone, these questions can help you find the right fit:
How many Amazon or Shopify sellers are currently in your client base?
Can you walk me through what economic nexus means for FBA sellers?
How do you handle multi-state sales tax for businesses using FBA?
Do you do ongoing tax planning throughout the year, or primarily year-end filing?
How do you track cost of goods sold for product resellers?
How do you reconcile 1099-K discrepancies?
An experienced eCommerce tax professional will answer these confidently and will likely ask questions of their own — about your platforms, fulfillment setup, and business structure. That back-and-forth is a good sign you've found someone who genuinely understands your business.
What Life Looks Like With the Right Systems
After working through the audit, our client built a setup that's been running smoothly since. Here's what it looks like:
They work with a team — Tall Oak Advisors — that focuses specifically on eCommerce. People who understand Amazon fees, FBA inventory, and multi-state compliance as a normal part of their day. They meet four times a year for planning conversations, not just once at filing time.
Link My Books connects directly to their Amazon and Shopify accounts and syncs everything into QuickBooks automatically. The books stay current month to month instead of being reconstructed all at once before a deadline.
Sales tax runs on a schedule. Obligations are tracked, amounts are calculated, and filings go out on time. They haven't had to manage a sales tax form manually in two years.
Quarterly payments happen automatically. A set amount moves into a tax savings account each month and goes to the IRS on schedule.
Total annual cost: about $7,500 for the team, software, and tools.
Estimated annual savings from better deductions and avoided penalties: $12,000–15,000.
The Bottom Line
eCommerce taxes have a lot of moving pieces — and the right support makes a real difference in how much you keep and how smoothly things run.
Tax software works well for straightforward returns. Once you add FBA inventory, multi-state sales, and business deductions, the complexity grows — and so does the cost of gaps in your records.
Our client's experience cost $47,000. With professional support over those five years, the cost would have been closer to $10,000 — and they would have kept significantly more of what they earned.
Your business has come a long way. It deserves books and tax strategy that keep up with it.
Ready to see what smarter eCommerce tax planning looks like for your business? Tall Oak Advisors works exclusively with online sellers — Amazon FBA businesses, Shopify stores, and eCommerce owners ready for a more strategic approach. FBA fees, multi-state sales tax, inventory tracking, and 1099-K reconciliation are what we do every day.
