If the purchaser has an address in an area with taxes, you then pay it. If they do some weird VPN workaround and billing address in the Cayman Islands, then you don't pay the taxes. It's self compliance. We sent men on the moon in 1969, this isn't rocket science to calculate a tax bill.
It's really interesting to think about this. Very different types of complexity.
The smallest possible correct program implementing a tax calculator is going to be a LOT bigger than the smallest possible correct program for controlling a 60's era manned flight to the moon. The latter is more complex in other ways, of course.
Complexity can be "deep" or "wide". software for rockets is "deep and thin complexity", but calculating hyper-local minimal tax bills is extreme "wide and shallow complexity".
