Arbitrage is the practice of buying an asset in one market and selling it in another where the price is higher, pocketing the difference. It works because identical things don’t always cost the same everywhere: information moves unevenly, stores misprice goods, and exchanges in different places quote different rates for the same currency or coin. Anyone quick enough to spot a gap and act on both sides of it can capture the spread.
The concept applies across financial markets, cryptocurrency exchanges, and physical retail stores. The mechanics of the trade look the same in each setting; the assets, the speed, and the tax treatment change.
How the Price Gaps Open and Close
Economists call the underlying principle the law of one price. Identical goods should trade at a single price in an efficient market. They often don’t, and each gap is a short-lived opportunity.
You buy where the asset is cheap and sell where it is expensive, ideally at the same moment. Your buying pressure in the cheap market pushes that price up. Your selling pressure in the expensive market pushes that price down. As more traders notice the gap, the two prices converge and the opportunity vanishes. The trade stops making sense once transaction costs eat what remains of the spread.
That last point matters more than beginners expect. The gross gap between two prices is not the profit. Fees, shipping, transfer times, and taxes all take a cut before anything reaches you.
Financial Market Arbitrage
Currency Arbitrage
Currency arbitrage exploits exchange rate discrepancies in the foreign exchange market. The simplest version finds a currency pair quoted at slightly different rates by two banks or brokers. Triangular arbitrage is the more complex cousin: money routes through three currencies to end up with more than you started with. Gaps are measured in fractions of a cent, so profits per trade are tiny and only add up across thousands of rapid transactions.
Merger Arbitrage
When one company announces it will acquire another at a set price per share, the target’s stock usually trades below that announced price. The discount reflects the risk that the deal falls apart over regulatory objections, shareholder votes, or financing problems. A merger arbitrageur buys the target’s stock and often shorts the acquirer’s stock to hedge broader market moves. The profit comes from the spread between the market price and the deal price closing as the acquisition completes.
Cryptocurrency Arbitrage
Bitcoin and other cryptocurrencies often trade at different prices across exchanges because each platform has its own pool of buyers and sellers. A coin might be $100 cheaper on one exchange than another at the same moment. You buy on the cheaper platform and sell on the more expensive one. Speed is the challenge. Blockchain transfer times, withdrawal limits, and exchange fees can erase the gap before you close both sides of the trade.
Retail Arbitrage
Retail arbitrage takes the same idea offline. You buy discounted products from physical stores and resell them on e-commerce platforms where they command full price. Clearance aisles, liquidation centers, and seasonal markdowns are the primary hunting grounds. A toy marked down 70% at a local retailer might still sell for near-retail on Amazon or eBay because shoppers elsewhere can’t access that same discount.
Success hinges on sourcing. You need to consistently find products where the resale price, minus all fees and shipping, exceeds what you paid. Most sellers use smartphone scanning apps that read barcodes and pull real-time pricing, sales rank, and fee estimates from major marketplaces. Experienced sellers develop a feel for which stores, categories, and times of year produce the best margins, but the work is relentless. You are physically walking stores, scanning shelves, and hauling inventory.
Is Reselling Legal?
Federal copyright law protects the right to resell products you have legitimately purchased. Under the first sale doctrine, once you lawfully acquire a copyrighted product, you can resell it without the copyright holder’s permission.1Office of the Law Revision Counsel. United States Code Title 17 Section 109 – Limitations on Exclusive Rights: Effect of Transfer of Particular Copy or Phonorecord You bought it, you own it, you can sell it.
Marketplace platforms add their own layer of rules. Some brands aggressively file intellectual property complaints against third-party sellers even when the products are authentic. These fall into three categories: trademark claims about how you use the brand name or logo, copyright claims about product photos or descriptions, and patent claims about protected designs. Even if you are legally in the right, fighting these complaints takes time and can result in listing removals while you appeal.
Certain product categories on major marketplaces require pre-approval before you can list items. Dietary supplements, medical devices, grocery items, and some electronics typically need documentation such as invoices from authorized distributors, safety certifications, or lab test results. Listing restricted products without approval can lead to inventory seizure or account suspension.
What Actually Eats the Spread
Platform fees take a significant cut. Amazon charges a referral fee on each sale, and most categories lose 15% of the sale price right off the top. Fulfillment by Amazon adds fulfillment fees based on size and weight, plus monthly storage fees for warehouse space.2Amazon Seller Central. 2026 US FBA Fulfillment Fee Changes Starting in April 2026, Amazon is adding a 3.5% fuel and logistics surcharge on top of standard FBA fulfillment fees.
Shipping costs add up whether you use FBA or fulfill orders yourself. If you ship directly to customers, residential delivery surcharges alone run $3.55 to $4.00 per package through major carriers, with more added for oversized or heavy items.3UPS. UPS Small Business Rate Guide Scanning apps, marketplace subscriptions, packaging, and gas for store runs all chip away at margins. Many new sellers discover their apparent 50% markup actually produces a 10% net margin after fees.
On the financial side, the equivalent drags are exchange fees, spread costs, and margin requirements. If you day trade in the U.S. and execute four or more day trades within five business days, and those trades exceed 6% of your total trades in that period, FINRA classifies you as a pattern day trader. That designation requires at least $25,000 in equity in your margin account at all times.4Financial Industry Regulatory Authority. Day Trading
How Arbitrage Profits Are Taxed
Every form of arbitrage generates taxable income, and the treatment splits along a clear line: financial trades are usually capital gains, and retail reselling is business income.
Profits from selling securities you held for less than a year are short-term capital gains, taxed at your ordinary income rate. Federal rates for 2026 range from 10% on the first $12,400 of taxable income for single filers up to 37% on income above $640,600.5Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 Since most arbitrage trades open and close within minutes or hours, virtually all financial arbitrage profits fall into the short-term category.
Retail arbitrage profits are not capital gains. The IRS treats reselling as business income, and most sellers report it on Schedule C of their personal tax return.6Internal Revenue Service. Instructions for Schedule C (Form 1040) You pay income tax on the profit after deducting the cost of the goods sold and ordinary business expenses like mileage, shipping supplies, platform fees, and software.7Office of the Law Revision Counsel. United States Code Title 26 Section 162 – Trade or Business Expenses
On top of income tax, self-employed resellers owe self-employment tax of 15.3% on net business earnings: 12.4% for Social Security and 2.9% for Medicare.8Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes) The Social Security portion applies to the first $184,500 of net self-employment income in 2026.9Social Security Administration. Contribution and Benefit Base Half of the SE tax is deductible when calculating adjusted gross income, but the full 15.3% still catches most first-year sellers by surprise. It is the single largest reason apparent scanning-app “profit” does not match the amount that reaches a bank account.
If you expect to owe $1,000 or more for the year, whether from trading or reselling, you are required to make quarterly estimated tax payments to the IRS covering both income tax and self-employment tax.10Internal Revenue Service. Estimated Taxes
Sales tax on marketplace sales is usually handled by the platform. Most states have marketplace facilitator laws requiring Amazon, eBay, Walmart Marketplace, and similar sites to collect and remit sales tax on behalf of third-party sellers.11Streamlined Sales Tax Governing Board. Marketplace Facilitator State Guidance Selling through your own website or at local events puts sales tax collection back on you.