There are two types of taxes here: sales tax and use tax.
Generally, a seller is required to collect the sales tax from the buyer and then remits that to the state. The seller can pass on collecting the tax but is still required to remit the amount to the state.
One of the exceptions is in interstate commerce. The seller is not required to collect sales tax in interstate commerce.
In the case of interstate commerce, the buyer is required to remit the tax to the state. In this case, it is called a use tax.
Interesting. How long until a state gub'mint stumbles on to charging a sales tax on the seller and a use tax on the buyer so they can garnish even more money? Do not put it past Demos to try such a thing.