Which country is that? The Netherlands, Austria and Germany, for example, all have horrible trafficking problems. In Nevada, the women are ostracised and harrassed by the police at the legal brothels. In New Zealand, the police cannot tell the difference between legal prostitution and illegal pimping.
So which country are you in that is doing better than these with legalised prostitution?
Well in Germany the main trafficking problems is Africans. They need to work something and because our rotten legal system prohibits them from working for months after they have arrived, the men end up dealing pot and the women on the streets.
And Romanian/Bulgarians... well, the men work on day-jobs for ultra low pay, often illegal, and the women go on the streets. Everything's better than the conditions where they come from.
Also, https://en.wikipedia.org/wiki/Human_trafficking_in_Germany links to a US Trafficking in Persons Report 2010. Here are some quotes:
"Ninety percent of identified victims of trafficking for commercial sexual exploitation came from Europe, including 28 percent from Germany ..."
"... approximately one third of identified sex trafficking victims reported that they had agreed initially to engage in prostitution."
"Police estimate that gangs brought around 1,000 Chinese people to Germany over the past decade and forced them to work in restaurants under exploitative conditions."
So, just like every other country then?