I read an interesting article on the Irish Times news app on my iPhone today. I can't find it now again nor can I find the article elsewhere so I can't provide a link.
In Germany where prostitution is legal the authorities have come up with a way of ensuring taxes are collected from the ladies, or the ones on the streets at least. Parking meter style things have been placed on certain streets and if a lady wants to work that street then she must purchase a 24-hour permit from the meter at a cost of €6. The police can stop a lady and ask her to produce her permit. If she doesn't have one then they'll do her for tax evasion.
Had to laugh when I read it. What a different reality to the way things are here.