Just look at what is happening in Florida right at this very minute. Specific items are exempt from taxation for a certain period of time. This week it is Hurricane supplies. Right before school starts it is clothing. Noble things for a benevolent state to do, right? Well, look closer at the list of things and you will see the complexity involved of "this item good (exempt)" "that item bad (non-exempt)." But that is a non-tax, you say. Sure, but look at the infrastructure at every cash register necessary to implement it. Can't you see how easy it would be for a group to decide that if you can exempt an item, you can also impose a variable rate? Piece of cake! The idea of classifying commodities for tax purposes isn't new at all. It only takes the will to implement guberment policy to start deciding how to use the tax code to influence individual behavior. Right now it is a pretty blunt instrument but the "fair tax" will turn it into a laser scalpel in comparison.
But this is already handled by EXISTING state infrastructure. Assuming that the Federal sales tax is done as a "pass-through" by means of the already-existing state infrastructure, then no new infrastructure will be necessary, and the existing IRS infrastructure can shrink drastically.
Even if there "is" added complexity, it is simply handled by a few added fields of computer code in the cash register computers that ALREADY handle the state systems.
The bottom line is that the Fair Tax will be "transparent" to the "end-user" who pays the tax. All he or she will see is just exactly what he sees today on the cash register slip---total sales, sales tax, and final total. No need to fill out forms and calculate even the "flat tax".