A small number of agents charge a reading fee just for looking at your work. Many literary agencies charge for long distance phone calls, photocopying, messenger services and other incidental expenses made on the author's behalf. These are costs you should ask about before you work with an agent. Most literary agencies also receive a 20 percent commission on foreign sales because they have to give a portion of the commission to the overseas agent. For this, these agents can receive up to a 50 percent commission.
Different agents do different things.
Agents pitch your proposal or manuscript to publishers, try to get you the best deal, and negotiate your contract. They manage your business affairs with a publisher once the book is sold. Some agents actually edit their clients' book proposals, and give other substantive assistance as the proposal is being crafted. The answer to that question could take pages. Because agents have had long relationships with particular publishers and editors, an agent can sell a proposal faster than a writer can.