If you're talking about a national sales tax (a tax on goods and services at the point of delivery), I don't see how that would stop offshoring, unless you're saying that we tax offshoring MORE. If that's the case, then my "blended" argument holds even more.
Some of that stuff is simply not traceable, or a company can offset the additional tax by offshoring MORE.
Come-on guys, this is not that hard. There is a charge when you invoice for the product or service, but FIRST FIRST FIRST get this: You take off of domestic products the overhead cost from personal and corporate incone tax. Now every product will have a commodity tax added to cover the burden of selling here. This will then be the elusive level playing field everyone always wanted to find.