Prostitution is mostly rape and should be regarded as such.

Underage prostitutes (which are extremely common in Europe) can't consent.

Drug addicts can't really consent.

Illegal immigrants can't really consent (because they can't refuse).

Prostitutes that are kept in a slave-like relationship can't really consent.

In richer countries the price you would have to pay even a low-income woman to do this would be so high, that almost noone would pay it. This "economic" gap is then filled by employers who manage to hold the "cost of labor" down by any means neccessary.

Yes, there is such a thing as completely voluntary prostitution. But the johns can't tell which from which. Especially in the lower price ranges you just have to assume a certain degree of exploitation and abuse from pimps if not from the johns...