Dear Aarti,
It differs from agency to agency; usually, 8.33% is preferred by both employer and client. 8.33% is a magic figure, equivalent to one month's gross salary. If placement is done for an Executive position, sometimes it varies from 10-12% of the gross annual salary. Usually, all employers seek a free placement of a candidate if the candidate leaves the organization within 6 months.
If you want recruitment to be done in African countries like Nigeria or Morocco, usually agencies charge some amount to be deposited as an initial deposit so that if at any point the recruitment is canceled, the amount is not refunded (getting the price for the work---in other sense). If the recruitment is completed, this amount is adjusted with the final payment.
The payment of the amount is usually done within 30-45 days by the employer after receiving the invoice (sometimes only after 45-60 days after the candidate joins the organization).
To cut the story short, it all depends on the organization's policy.
Suresh
mgsuresh@gmail.com