Sales tax is the tax system small businesses meet earliest and understand last. Unlike income tax, it is transactional: the state authorizes you to collect it (the seller's permit), expects you to collect it correctly on every taxable sale, and treats the collected money as its own from the moment it hits your account. The permit itself is easy; knowing where you owe one, and keeping up with the filing rhythm afterward, is the actual work.
Nexus Decides Where You Register
You need a permit in every state where you have nexus, the legal connection that lets a state tax you. Two kinds matter:
Physical nexus is presence: your location, employees, inventory (including inventory a marketplace stores for you in its warehouses), regular in-person sales, even trade show attendance beyond thresholds in some states. Your home state is always on the list.
Economic nexus arrived with the Supreme Court's Wayfair decision: enough sales into a state creates the obligation with no physical presence. Most states set the threshold at $100,000 in annual sales or 200 transactions (several have dropped the transaction count; California and Texas use $500,000). Cross a threshold, and registration is due, usually within a defined window. The full mechanics, with the threshold logic explained, are in sales tax nexus explained.
The practical sequence for a new seller: register at home before the first sale, then monitor out-of-state revenue by state and register as thresholds approach. Waiting until a state finds you converts a free registration into a back-tax assessment.
Marketplace Facilitator Laws Changed the Math
Every state with a sales tax now has a marketplace facilitator law: Amazon, Etsy, eBay, Walmart, and similar platforms must collect and remit sales tax on your marketplace sales themselves. For pure marketplace sellers this removes most collection work, with two caveats that catch people. First, several states still require the seller's own registration (and returns reporting marketplace sales as excluded) once nexus exists, particularly where FBA inventory creates physical nexus. Second, the moment you add a direct channel (your own site), collection on those sales is entirely yours. Mixed-channel sellers live in both worlds and should map obligations per state rather than assume the platform covers everything.
Registering, Then Operating
Two operating details deserve emphasis. Destination sourcing: most states tax by the buyer's location for remote sales, which is why rate automation (built into modern checkout and accounting stacks) beats manual tables. And the trust-fund principle: collected sales tax is the state's money in your custody, in the same personal-liability category as payroll withholding. It is never working capital.
The Mistakes That Generate Assessments
Why it happensThe permit feels like paperwork that can follow revenue.
ConsequenceUncollectable back tax paid from margin, plus penalties for unpermitted sales.
PreventionRegister at home before the first taxable sale; it is free almost everywhere.
Why it happensOut-of-state sales accumulate quietly under many state thresholds.
ConsequenceMulti-state back-tax exposure discovered years later, often at diligence time.
PreventionTrack sales by state quarterly; register as thresholds approach.
Why it happensNo sales, so surely no filing.
ConsequenceLate-filing penalties on empty returns, and eventually permit revocation.
PreventionEvery assigned period gets a return; automate or calendar them.
Why it happensWholesale buyers say "we're exempt" and the invoice goes out untaxed.
ConsequenceThe auditor assesses you for every undocumented exempt sale.
PreventionCertificate collected before the first untaxed sale, renewed on the state's cycle.
One Seller, Two Channels
A Texas maker sells on Etsy (facilitator collects) and her own site (she collects). She registers in Texas pre-launch, configures destination-based rates at checkout, and watches state-by-state totals quarterly. When California direct sales approach the threshold, she registers there before crossing it.
Outcome: Zero assessments, because registrations preceded obligations. The entire system ran on one quarterly review.
Register where nexus lives, file every period, never spend the tax
The permit is the easy part. The discipline is knowing where your sales create nexus, filing on every assigned date including the empty ones, and treating collected tax as the state's money from the moment of sale.
Frequently asked questions
What is a seller's permit?
The state registration (also called a sales tax permit, sales and use tax license, or resale license depending on the state) that authorizes a business to collect sales tax from customers and remit it. It is required before making taxable sales in a state where you have nexus, and registration is free or cheap in most states.
Do I need a seller's permit for an online business?
Yes, wherever you have nexus: always your home state (physical presence), plus any state where your sales cross economic nexus thresholds, commonly $100,000 in sales or 200 transactions per year since the Wayfair decision. If you sell only through marketplaces like Amazon or Etsy, facilitator laws shift most collection to the platform, but some states still require your registration.
How much does a sales tax permit cost?
Free in most states; the exceptions charge modest fees (commonly $5 to $100, and a few require deposits). The real cost is the ongoing obligation: collecting correctly, filing on the state's assigned frequency even for $0 months, and keeping exemption certificates for wholesale sales.
What is the difference between a seller's permit and a resale certificate?
The permit lets you collect tax from your customers. A resale certificate is what you hand your suppliers to buy inventory tax-free, because tax will be collected on the final sale. You generally need the permit first; the certificate quotes its number. Using resale certificates for non-resale purchases is a fast route to an audit.
What happens if I sell without a permit?
States assess the uncollected tax against you personally plus penalties and interest, and selling without a permit is itself an offense in most states. Since you cannot retroactively collect from past customers, the tax comes out of your margin. Registering late is always cheaper than being found.
How often do I file sales tax returns?
The state assigns monthly, quarterly, or annual frequency based on your volume, and adjusts it as you grow. Returns are due even for zero-sales periods once registered; skipping a $0 return still generates penalties in most states. Software or your compliance calendar should carry every assigned date.
Do service businesses need seller's permits?
Depends on the state and the service. Most states tax tangible goods and a defined list of services (repair, lodging, digital goods increasingly). Pure professional services usually stay exempt, but mixed transactions (a designer selling printed materials) often cross the line. Check your state's taxable-services list before assuming exemption.
Selling taxable goods? Register before the first sale.
Entity, EIN, and the state registrations lined up in the right order, with compliance monitoring tracking every filing frequency the states assign you.
