Absolutely, it's common, but as I said
they aren't always forced into it
"Aren't always" means sometimes. There are brothels in Nevada in which the woman do it of their own free will and make 10 to 20 thousand dollars a month. That doesn't make it right or less immoral, but they are anything but victims.
I would think the supposed victims far outweigh those you claim who aren't.
But I view any women who chooses to live a life as a prostitute as a victim.
It all depends upon your point of view.