Sales Tax Nexus
Sales tax nexus is a connection with a state significant enough that the state can require you to register, collect and remit its sales tax. It comes in two flavors: physical nexus, created by inventory, employees, offices or contractors in the state, and economic nexus, created by crossing a sales threshold. For FBA sellers the big one is inventory: Amazon moving your stock into a state's warehouse creates physical nexus there whether you asked or not.
Nexus is where ecommerce sellers accumulate invisible liability. An FBA seller's inventory routinely spreads across 20-plus states within months of enrolling, and each of those states has a claim. Marketplace facilitator laws blunt the damage, Amazon remits tax on its own orders, but they don't erase registration obligations everywhere, they don't cover your Shopify sales in those states, and a few states levy gross receipts taxes like Washington's B&O that the marketplace never pays for you.
The right response is triage, not panic: figure out where real dollars are at stake, register there, and skip the states where exposure is trivial. Registering everywhere costs more in filing fees than the tax. We run that analysis inside our ecommerce tax services, and our state guides for Washington and Florida show how different the rules can be.
Where this shows up in our work
This isn’t textbook material for us; it’s the day-to-day of keeping seller books right. See how we handle it in practice:
Ecommerce Tax Services→Related terms