Groups like Save the Children and ActionAid estimate there are 2,300 placement agencies in Delhi alone, and less than one-sixth are legitimate.
"There are so many agencies and we hear so many stories, but we are not like that. We don't keep the maids' salaries and all are over 18," said Purno Chander Das, owner of Das Nurse Bureau, which provides nurses and maids in Delhi's Tughlakabad village.
The Das Nurse Bureau is registered with authorities - unlike many agencies operating from rented rooms or flats in slums or poorer neighbourhoods like Shivaji Enclave in west Delhi. It is often to these places that maids are brought until a job is found.
There are no signboards, but neighbours point out the apartments that house the agencies and talk of the comings and goings of girls who stay for one or two days before being taken away.
"There is at least one agency in every block," says Rohit, a man in his twenties, who lives in one of scores of dilapidated government-built apartment blocks in Shivaji Enclave.
With a commission fee of up to Rs 30000 and a maids' monthly salary of up to Rs 5000, an agency can make more than $1,500 annually for each girl, say anti-trafficking groups.
A ledger recovered after one police raid, shown by the charity Bachpan Bachao Andolan to Thomson Reuters Foundation, had the names, passport pictures and addresses of 111 girls from villages in far-away states like West Bengal, Jharkhand, Assam and Chhattisgarh, most of them minors.
Image Courtesy: Bachpan Bachao Andolan