The honest answer is: it depends on where you sell and how big you intend to get, but most marketplace sellers reach a point where registration becomes practically necessary faster than they expect.
The general principle
You can generally test an idea as a sole proprietor (using your own name/SSN) in many jurisdictions without formally registering an LLC — this is the lowest-friction way to validate a product idea (see How to Validate a Product Idea). But this is not the same as "no obligations": you still owe income tax on profit, and depending on your state and revenue, you may still need a local business license.
Why marketplaces push you toward formal registration anyway
Amazon, Walmart, and other marketplaces increasingly require business verification (a legal business name, tax ID, and matching bank account) as part of their own seller approval process — see each marketplace hub for specifics. In practice, this means most sellers end up registering a business entity (even a simple single-member LLC) within their first months, not because it's strictly required to make a first sale, but because it's required to pass marketplace approval and to separate personal and business liability once real inventory and revenue are involved.
What "testing as an individual" actually covers
Testing as a sole proprietor is most defensible for the earliest, smallest-scale validation: a handful of sample sales, a very small test batch, or a marketplace category (like many Etsy shops) that's built around individual/handmade sellers. It becomes a poor fit quickly once you're placing real inventory orders, hiring any help, or applying to a marketplace that requires business documentation upfront (Amazon and Walmart both commonly do, depending on category and account type).
When to prioritize registering before you even test
If your product category carries real liability risk (anything ingested, applied to skin, used by children, or that could cause injury), or if you're bringing in a business partner, formalize the entity before you sell — the liability protection matters from the first unit, not just once you're bigger. See Business Insurance for Ecommerce Sellers for the related coverage question.
A simple sequencing guide
- Idea stage, no sales yet: research and validate as an individual; no registration needed to research.
- First small test sale(s), low-liability product: sole proprietorship is commonly acceptable, but confirm your state/local requirements.
- Ready to place a real inventory order, or the product carries liability risk: register an entity (see Sole Proprietorship vs. LLC vs. Corporation) before that order ships.
- Applying to a marketplace that requires business verification: have your entity, EIN (if applicable), and matching business bank account ready before starting the application — see What You Need Before You Apply.
What doesn't go away regardless of structure
Even as a sole proprietor with no formal registration, you're still responsible for reporting income and paying applicable taxes, and depending on your product and location, you may still need specific permits (a local business license, a seller's permit for sales tax purposes, or a category-specific certification). "Not registered" is not the same as "no obligations" — see Business Licenses and Permits.
Next step
If you decide to formalize, Sole Proprietorship vs. LLC vs. Corporation walks through picking a structure.