Journalist Ross Ramsey wrote for The New York Times 18 December 2014:
-----------------------------------------------------------------------------------------
The goods you buy online and through mail-order catalogs from out of state are not tax free. It’s just that the state has a hard time collecting the taxes that are due. Retailers do not pay sales taxes. Consumers do. Retailers just collect them and remit them to the state. And not all retailers are required to play. Texas has no way to force sellers in other states to collect taxes. The retailers that are not required to collect the taxes — a group that includes out-of-staters who sell online and through mail-order catalogs — are not the ones violating state tax laws.

Consumers are the deadbeats, and hardly anyone in politics wants to go door to door to straighten them out. ...Texas and other states have been trying for years to get the federal government to set up a system to get retailers all over the country to collect the taxes and remit them.
-----------------------------------------------------------------------------------------

article

Retailers do not pay sales taxes. Consumers do.
And that is what's wrong with the system. Retailers should be PAYING the sales tax.

Every business is required to keep books and records, and to render them up for examination by the State at the State's discretion. In the case of Miles Laboratories v Simon (33 Federal Supplement 962), a case concerning the state sales tax, it is declared: "The tax has been held to be a privilege fee imposed upon persons doing business at retail. ...The tax is not imposed upon the consumer, but upon those 'engaged in the business of making sales at retail, as hereinbefore defined.'"

It was also noted that the company has the option of adding the sales tax amount to the receipt or not to. Some stores have a fixed price on their goods, and when you go to the register to pay, the price that is on the price tag is the price that is charged. The tax that the company is liable for has already been included in the price as a cost of doing business. Most stores, however, calculate the tax and place it on the receipt, making it appear that the customer is the one liable for the tax.

Concerning an internet sales tax, governments are making a problem where one doesn't exist. Companies that make sales on the internet can make their sales the same as they would in their brick-and-mortar structures, with the sales taxes embedded into the price of the product as a cost of doing business. When they make a sale on the internet, it doesn't matter where the item is going. When the company makes their reports to their State, they send the money for the amount of the tax imposed upon them by that State.

It's not really all that complicated.

Example: An item that you want is found on Amazon.com. It is shipped from a supplier in the State of Washington to you in Michigan.

From the Washington State Sales Tax site:
The seller is liable to the Department of Revenue for sales tax, whether or not it is collected.
With the tax system being promoted in the congress, you will pay Washington sales tax, and Michigan sales tax also. Now, how fair is that? It's a double taxation.