There's a reason why money for service is the oldest profession. Ignoring the drugs, trafficking, judiciary, and "ethical" aspects, it's a simple, honest exchange between two individuals.
It's when opportunists in the black market and the "white market" (i.e. laws and regulations, etc.) try to get a piece of the profit or a semblance of control that things worsen for sex workers, and, in turn, the overall quality of experience for sex workers and johns alike.