E-Commerce & Online Seller Tax Services

Online selling has a low barrier to entry but a high complexity ceiling once you scale. Between multi-state sales tax compliance, platform 1099-K reporting that doesn't match your actual income, inventory accounting across multiple warehouses, and international sourcing, e-commerce tax mistakes compound quickly. Myung Keon Kim CPA works with Amazon FBA sellers, Shopify store owners, eBay sellers, and multi-channel merchants who need accurate books and a proactive tax strategy.

Multi-State Sales Tax Compliance

The post-Wayfair world requires every online seller to monitor their sales volume in each state and register for sales tax collection once they cross the economic nexus threshold. For sellers using Amazon FBA, the analysis is more complicated: Amazon stores inventory in fulfillment centers across the country, which creates physical nexus in those states — meaning you may have nexus in states like Texas, Pennsylvania, and Illinois simply because Amazon is storing your inventory there.

Marketplace facilitator laws have shifted much of the collection burden to platforms in most states. Amazon, eBay, and Etsy now collect and remit sales tax on behalf of third-party sellers in nearly all states. However, Shopify, WooCommerce, and other direct-to-consumer channels do not have this obligation — you do. A seller running both an Amazon storefront and a Shopify store must analyze nexus and compliance for the Shopify channel independently of the marketplace channel.

Inventory Accounting — FIFO, LIFO, and Weighted Average

Cost of goods sold (COGS) is the largest expense deduction for most product-based businesses, and the accounting method you choose determines how much of your inventory cost is deducted in any given year. FIFO (First In, First Out) assumes you sell your oldest inventory first — in an inflationary environment, this results in lower COGS and higher taxable income. LIFO (Last In, First Out) assumes the newest (and most expensive) inventory is sold first, resulting in higher COGS and lower taxable income. LIFO is only available for US federal tax purposes — it is not accepted under international accounting standards and requires a Form 970 election. The weighted average method averages all inventory costs and is the simplest to administer.

For e-commerce sellers sourcing from overseas (China, Korea, Vietnam), import costs — including customs duties and freight — are part of your landed cost and must be included in inventory valuation. Getting this wrong understates COGS and overstates income.

Platform 1099-K Reporting

Public Law 119-21 (July 2025) repealed the lower reporting threshold introduced by the American Rescue Plan. Under IRC §6050W(e) as it now stands, a third-party settlement organization must file a 1099-K only where your gross payments exceed $20,000 and your transaction count exceeds 200 — both conditions, not either one. This de minimis applies only to third-party settlement organizations: payment card transactions carry no threshold, so card-settled sales are reported from the first dollar regardless of volume. In practice you will still receive 1099-Ks from Amazon, PayPal, Shopify Payments, Venmo for Business and other processors.

The critical mistake many sellers make: reporting the 1099-K total as income. The 1099-K reports gross payment volume — it includes sales tax collected by the platform on your behalf, items you refunded, and the pre-fee amount before Amazon deducts its selling fees. Your actual taxable income is gross sales minus returns and allowances minus COGS minus business expenses. We reconcile your 1099-K amounts against your actual income to ensure you are not overpaying tax on pass-through amounts.

Estimated Quarterly Tax Payments

E-commerce sellers are self-employed, which means no employer is withholding taxes from your income. The IRS requires quarterly estimated tax payments if you expect to owe $1,000 or more in tax for the year. Payments are due April 15, June 15, September 15, and January 15. Failure to make sufficient estimated payments results in an underpayment penalty — the IRS charges interest on the shortfall for each quarter it occurred.

For e-commerce businesses with seasonal sales (heavy Q4, slower Q1–Q2), annualizing income using the IRS Form 2210 annualized income installment method can reduce the required Q1 and Q2 payments, which is important for cash flow management when you are rebuilding inventory after the holiday season.

International Sourcing and Customs Duties

Many e-commerce sellers source products from overseas manufacturers. Import duties, customs broker fees, and international freight costs are part of your inventory's landed cost — they are capitalized into inventory and deducted as COGS when the inventory is sold, not when you pay them. This distinction matters: paying $30,000 in tariffs in December does not produce a $30,000 deduction if the inventory is still unsold at year-end.

Section 301 tariffs on Chinese goods, Section 232 steel and aluminum tariffs, and antidumping duties add significant cost to many product categories. We track your landed cost per unit and ensure your inventory records accurately reflect the full cost of bringing goods to market, which maximizes your COGS deduction as you sell through inventory.

Business Structure for Online Sellers

Many online sellers start as sole proprietors and quickly realize they have grown into something that benefits from entity protection and tax optimization. A single-member LLC provides liability protection without changing how you are taxed (still Schedule C by default). An S-Corp election becomes attractive once your net profit consistently exceeds $80,000–$100,000, reducing self-employment tax on the distribution portion of your income. We analyze your current income trajectory and recommend the appropriate structure before the savings opportunity is lost.

Frequently Asked Questions

Do I need to collect sales tax in every state I sell to?

Not necessarily, but you need to analyze each state separately. After the Supreme Court's 2018 South Dakota v. Wayfair decision, states can require out-of-state sellers to collect sales tax based on economic nexus — typically $100,000 in sales or 200 transactions in a state, without any physical presence. Most states have adopted economic nexus thresholds, though the exact numbers vary. Some states (like Amazon's marketplace facilitator states) require the platform to collect and remit tax on your behalf, which reduces your direct obligations. However, you still need to track your nexus exposure in states where you sell direct, through your own Shopify store, or where the platform does not act as a facilitator.

How do I report my Amazon 1099-K income?

Amazon issues Form 1099-K reporting your gross sales processed through their payment system. The 1099-K figure is gross — it includes sales tax collected on your behalf, refunds you processed, and Amazon fees that were netted out before you were paid. You do NOT report the 1099-K amount as income. Instead, you report your actual gross sales, subtract returns and allowances, subtract cost of goods sold, and deduct all allowable business expenses (Amazon fees, shipping, advertising, storage). The 1099-K amount will typically be higher than your taxable income — and explaining that discrepancy to the IRS requires clean records.

Can I deduct my home office as an online seller?

Yes, if you use part of your home regularly and exclusively for your e-commerce business. The home office deduction under IRC Section 280A allows you to deduct a proportionate share of your home expenses — rent or mortgage interest, utilities, insurance, and depreciation — based on the square footage of the dedicated business space. If you also use a portion of your home for inventory storage, a separate storage area deduction may apply even without the "exclusive use" requirement, as long as your home is your only fixed location for the business. The simplified method allows $5 per square foot up to 300 square feet without calculating actual expenses.

What is economic nexus and when does it apply to me?

Economic nexus is a sales tax concept that allows states to require remote sellers to collect and remit tax based solely on their sales volume or transaction count in the state — without physical presence. Following the Wayfair decision, every state with a sales tax has adopted economic nexus rules. The most common threshold is $100,000 in sales or 200 separate transactions in a 12-month period, but some states have lower thresholds or use different calculation methods (e.g., California's threshold is $500,000 with no transaction count). Once you cross a threshold, you typically have 30–60 days to register and begin collecting. Marketplace facilitator rules mean Amazon, Etsy, and eBay collect for you in most states, but Shopify direct sales are entirely your responsibility.