You really want to make a comparison between modern slavery and wwoofing?
Two bits of info to help you think about it:
Victoria's odyssey began when she was 17, fresh out of school in Chisinau, the decayed capital of the former Soviet republic of Moldova. "There was no work, no money," she explained simply. So when a friend—"at least I thought he was a friend"—suggested he could help her get a job in a factory in Turkey, she jumped at the idea and took up his offer to drive her there, through Romania. "But when I realized we had driven west, to the border with Serbia, I knew something was wrong."
It was too late. At the border she was handed over to a group of Serb men, who produced a new passport saying she was 18. They led her on foot into Serbia and raped her, telling her that she would be killed if she resisted. Then they sent her under guard to Bosnia, the Balkan republic being rebuilt under a torrent of international aid after its years of genocidal civil war.
Victoria was now a piece of property and, as such, was bought and sold by different brothel owners ten times over the next two years for an average price of $1,500. Finally, four months pregnant and fearful of a forced abortion, she escaped. I found her hiding in the Bosnian city of Mostar, sheltered by a group of Bosnian women.
UN officials have reported that as many as 3000 women and children fleeing religious persecution in Iraq have been captured and may be at risk of modern slavery by the Sunni extremist group that is rampaging through parts of Iraq and Syria.