Just wanted to share an email I received from a writer I contacted for advice:
Hi Ms. Holt,
Thank you for your kind words about my story.
I’ve been very happy with my agent but I know her list is getting full and she doesn’t often take on new clients. I think she signed on just three in the last year, but you can learn more about her and how she does business from her blog.
As you learn about the business, know that a good agent should never be paid unless you’re paid first, when they take a percentage of the money your publisher pays you — usually 15-20%. If they don’t sell your book to an advance/royalty-paying publisher, they don’t make money because a good agent doesn’t charge any fees. A good agent will more than earn her commission because she will likely get that much more in advance money than you’d get negotiating the deal yourself. But agents do more than just sell your book — they negotiate the contract, make sure the publisher pays you, target the right publisher for your book because of their business contacts, provide career advice, and are an advocate for you (the publisher is your client, the agent is like your business partner), among many other things.
Best wishes in your future endeavors.
The Big 6 publishers generally don’t accept submissions directly from writers, anyway, so you’ll need an agent if you hope to go the big publisher route. Many medium and small publishers don’t require submissions via an agent, so before you begin the agent search, you might want to study the publishing business and determine whether your manuscript would be better suited to a smaller publisher. If so, you may be able to bypass the agent search altogether, as many agents don’t sell to smaller publishers since they tend to pay smaller advances and it wouldn’t be a lucrative effort for an agent. This is one reason the smaller publishers don’t require use of an agent.
Agentquery.com is a good source for finding reputable agents — I think they screen agents pretty well before including them on their site. Their section for writers also has good information about the publishing business and tips on the query process. A well-researched list of bad agents can be found at Writer Beware. They also have lots of information on how the business works.