There is a big difference. The way Always Right wrote it up, if you purchased a $100 item you would pay $130 (he then jumped it to $137 because he claims that states would have to drop their income tax and switch to a sales tax, which they won't).
And the reason it is different is because the tax inclusive (pay $100, retailer gets $70, gov. gets $30) comparrison is how you have to do it for an apples to apples comparrison with income taxes.
Just like with income taxes. And I'm using easy round numbers here for ease. If you earn $1,000 you send $300 to the government and keep $700. You don't keep $1,000 and then send $300 to the government.
In the end it works out the same either way, but for an apples to apples comparrison, one must used the tax inclusive method.
One problem with your numbers, PL... the $100 item would be $77 for the seller, $23 for the feds, not 70/30.
In a tax inclusive system, would the seller be required to itemize the taxes and products?
23% of $70 is $16.10. Total cost $86.10, not $100. Even 30% of $70 is $21 for a total of $91.
You make the assumption that the retailer who is currently selling a product for $100, will be happy to only get to keep $70. This is illogical. The retailer will continue to want to receive the same amount of money for his product, and, in order to do so, will raise the price so that after the tax, he still makes his $100.