The purchaser has always been responsible for the sales tax. However, in America, almost all taxing jurisdictions implement a withholding charge on the merchan

The purchaser has always been responsible for the sales tax. However, in America, almost all taxing jurisdictions implement a withholding charge on the merchant, so that the merchant collects the sales tax owed by the purchaser on the purchaser's behalf. Quill v. North Dakota, the SCOTUS case to which you refer, was about a sale-order catalog's obligation to withhold the sales tax for purchases by out-of-state state customers (in the case, customers in North Dakota). SCOTUS ruled that North Dakota did not have the jurisdiction to impose a withholding obligation on Quill because it did not do sufficient business in the state to have a "presence". However, after the case in various speeches, several of the deciding justices noted that if Quill had had a greater volume of business (on the order of an in-state retailer), the outcome would probably have been different.