In effect, they're playing the old profit vs. markup game, and a lot of silly sods are buying into it.
Quick example: Item costs $1.00 with the 'fair' tax applied. The Fair Taxers and their mythical 23% tell you gleefully that the item pre-tax costs just $0.77, thus 23%. However, if the pre-tax cost is $0.77, the $0.23 tax is a rate of 23/77, or 29.87%.
How appropriate that the Huckster likes this flim-flam, eh?
It's actually quite simple to understand.
23% inclusive is equivalent to 29.87 exclusive. If your point is that this is intended to fool anyone, well, who? Most of them are still in pre-K.
The best way to analyze the tax is to compare it to now. How would you do that?