> Physical businesses

Physical businesses nominally aren't selling their items to people across state or country borders.

Of course, we threw that out when we decided people could buy things online. How'd that tax loophole turn out?

But when they do, federal law requires age verification (at least with e.g. alcohol).

It turned out we pretty much closed the tax loophole. I don't remember an online purchase with no sales tax since the mid 00s.