I think I do understand, I think you are equating halachah with dina d’malchusa.
Technically one who purchases something from out of state has to report it and pay sales tax, even if the seller is not required to pay.
This is rarely, if ever, enforced, but I’ve seen the forms to report purchase (use) tax. I think this is what NDG is referring to.
From the tax.ny.gov site:
Use Tax for Individuals (including Estates and Trusts)
Tax Bulletin ST-913 (TB-ST-913)
Printer-Friendly Version (PDF)
Issue Date: Updated February 19, 2016
Introduction
New York State and local sales taxes are imposed on taxable property and services purchased or delivered to you in New York State. In most instances, when you purchase a taxable item or service in the state, or if it is delivered to you in the state, the seller will collect sales tax from you. The seller then pays the tax over to the Tax Department.
Use tax is a tax imposed on taxable items or services used in New York when the sales tax has not been paid. If a sales tax has not been collected by the seller on a taxable sale, or when taxable items or services are used in New York and the New York sales tax has not been collected, you must report and pay tax directly to the Tax Department. This bulletin discusses the circumstances when a resident of New York State would be required to pay tax on these sales and uses. There is a distinction between sales tax that should have been paid and use tax. However, for purposes of simplicity, the tax required to be paid is referred to in this bulletin as use tax.
The following are common situations in which a New York State resident may owe use tax:
purchases of taxable property or services made outside of New York State;
purchases of taxable property or services made over the Internet, from catalogs, or by phone from businesses that are located outside of New York State;
purchases of taxable property or services on an Indian reservation;
purchases where the taxable property or services are used in a different local taxing jurisdiction in the state from where they were purchased or where they were delivered.