And do those companies facilitate black market transactions that would be tax-free?

I would consider it a deferred tax. You pay iff you are caught by the tax man with interest (and a potential bonus of a tax free holiday in a state sponsored facility). Better arrangements may be available if you are rich enough so you can get experts to arrange your taxes being legally deferred effectively after you died.

It’s another wrinkle GP didn’t get to. If you are paid, how to launder the money? Presumably you’d get a shiesty lawyer to buy you a nail salon ala breaking bad.