However, the assertion is not baseless as your post connotes IMO.
Your first point, that an individual could present a falsified sales tax exempt form, is clearly true. But that is the case already today. WHile the nrst would not remove all chance for an individual to cheat alone, it is also the case that it becomes more difficult to do so. A sales tax exempt form can be forged or borrowed to be sure - enforcement of sales taxes is just as agressive as for income tax, and under an nrst the enforcement becomes much easier. So it doesn't seem to represent much of a change. Nevertheless, it is obviously true that this does and will always happen to some degree. Maybe we could meet in the middle on that one.
The second point, that a retailer may collect but not remit the tax, is possible too. But the retailer would then forfeit his portion of the collections - which would likely be insignificant on one sale but may be substantial in aggregate. And again, with enforcement being so much more efficient, it is much more likely that they would opt to not take the chance. But again, you are correct that this is a possible scenario - that also exists today. There are bagillions [mathematician's word for lots :0)] of retailers that charge full price for their product/service but who short the income tax man.
Anyway, good points, imo.
I know a person who has a legitimate business who uses his sales tax exemption cert to evade the 6% state sales tax. If the stakes were raised to 30%, I suspect that many people would create a 'business' out of their hobby. There would be significantly more legitimate sales tax exemption certs out there and they would be used fraudulently.
No jurisdiction in the world has a 30% sales tax. Evasion prohibits it.