The Quill ruling had meant that non-resident retailers selling to US consumers were largely exempt from having to charge state or local sales tax to their customers. But the South Dakota ruling extended this to merely selling remotely into the state. This is similar to the EU distance selling VAT rules, and many other countries around the world apply the same non-resident seller liabilities.
In addition to state sales tax, non-US Sellers may also have to consider the thousands of local sales tax jurisdictions. Companies will need to ensure they have adequate tracking of the exact location of their US customers, and what additional Sales Tax rates calculations, collections and filings will be required.
The Wayfair ruling included upholding a South Dakota sales tax registration threshold of $100,000 or if the seller has more than 200 individual transactions in the state. Most other states have implemented similar thresholds, ranging up to $500,000 per annum.