Many people are so desparate to leave Nigeria that they will trade with any dealer that offers transport.
This can be the result!!!        

Investigators went to Mali earlier this year and estimated that at least 20,000 Nigerian teenagers and women had been smuggled there and forced into prostitution.

The network of migration routes that criss-cross West Africa are known to police as a "hot graveyard for migrants", because the number who die on the way is so great.
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“Start Quote
Arinze Orakwue, Nigeria's National Agency for the Prohibition of Traffic in Persons

    What we want Mali to do is say: 'Nigeria, come! We will support you,  to get the girls back.'”

End Quote Arinze Orakwue Naptip

So-called "trolley-boys" - the trafficking middle-men - run "the relay race", passing their human cargo onwards, with promises of jobs in hairdressing and supermarkets.

The true nature of the "job" is revealed later.

After receiving reports of sexual slavery from aid workers and clergy, Nigerian officials went to Mali to investigate earlier this year.

They said were "nauseated" by what they had seen: Brothels with cubicles in which young Nigerian women, many in their mid-teens, serviced as many as 20 or 30 clients a night, in order to pay off debts incurred to the "trolley-men".

"It is clear it is not consensual," says Arinze Orakwue of Nigeria's National Agency for the Prohibition of Traffic in Persons (Naptip). "They have no freedom of movement. They are not allowed to go outside with you, or even to make a phone call."

Naptip's hard-hitting findings, published on 29 September, also warned of what officials described as "slave camps" in Mali's north - brothels in the gold-mining towns of Kayes and Mopti.

Photographs seen by the BBC reveal precise locations and buildings examined by the team.

BBC Report http://www.bbc.co.uk/news/world-africa-12068974

and here  http://news.bbc.co.uk/1/hi/world/africa/4481863.stm