Since South Dakota v. Wayfair, US states can require out-of-state sellers to collect sales tax once they cross an economic-nexus threshold — typically a dollar amount of sales, a transaction count, or both. Six years on, the thresholds still differ from state to state and continue to be adjusted.
Marketplace facilitator laws mean platforms like Amazon collect and remit tax on many sales, which helps — but it does not remove a seller's own obligations for direct sales, registrations already triggered, or historic exposure before the rules applied.
The recurring failure mode is silent threshold crossings: a seller grows into nexus in several states without registering, then faces back-tax and penalties. The fix is continuous monitoring, not an annual review.
Infiniti3 tracks economic nexus by state, flags thresholds before they're crossed, manages registrations and filings with deadline checking, and reconciles collected versus liable amounts.