Exactly. The "progressive tax" people will demand that "reasonable refunds" be made; just as the income tax was subverted by a host of "reasonable deductions", the FairTax will be subverted by a host of "reasonable rebates".
I wish the FairTax well. I hope it comes into play - not so much because I like it, but because ANY tax system becomes corrupt and must be replaced periodically.
The FairTax defenders are spending too much time saying "we've solved that" and not enough time creatively looking for ways to subvert it, as $XBs will rewarded to those who succeed in subverting whatever tax system is in place - and there WILL be loopholes.
Until the gov't returns to its roots of not taxing citizens, and not handing out money to them, there will always be room for corruption.
Even if they DO return to not taxing citizens, there will STILL be room for tax corruption and shennanigans - always will be ... by definition.
The definition of the prebate is written into the bill in a way that, to alter it an any meaningful way, would require a change of tax rate or a change in federal poverty definitional standards used in many govenment programs. Neither change is likely since a rate change affects taxes on everyone and cannot be hidden as at present and changing something used in many programs would be, as a practical matter, impossible.
The "progressive tax" people (whoever they might be) can yell till they're blue in the face to no effect. With enough votes to pass the bill, there will be sufficient political muscle behind it to overcome any such challenges.