Yes, you do have to give them a percentage of what you make on a contract and your royalties. On the other hand, they advise you and can get into the door of a publisher better than a writer can, especially a first time writer. There are many pros and cons and I would like to discuss some of them.
First of all you want an agent that will help you grow your business. Not only will they get your manuscript to the right people, but they should help you with other areas of your business.
You want an agent who is respected in the industry. I have heard a lot of horror stories about agents and on the other hand I have heard wonderful stories about them. Some about the same agent. We all have different personalities and can work with different people better. I would suggest everyone get to know several agents at conferences. One will stand out in your mind and you will be drawn to that person. If you read the ACFW loops, you will get an idea about which agents are better than others.
Is the agent friendly or only talks to certain people? I've seen that happen that some agents have certain groups that they want to talk to. To me, I want an agent that is outgoing with everyone. They are friendly and willing to take a moment to listen to you. I had one agent that seemed enthralled with what I was telling them about my book. That agent had good listening skills. I want an agent like that.
Can the agent offer you anything other than selling your book? Can they help you with good advice about further books? Do they encourage you to go out of your box with promotions? Are they really interested in your book selling or do they just want a paycheck themselves? I want someone who can help me. As a first time writer, I need help. I have found it in other authors and writers, but when it gets down to an agent, I want someone who believes in me and can take my interests at heart.
Do they read your proposal? A good agent will read it, I believe. I may be wrong, but I hope and pray that they do. Can they make suggestions? I live on suggestions and comments from other people. Some people can say one word that will make a difference in your journey.
When it comes time for that contract, will the agent explain the contract to you. Will they see that there is no mumbo-jumbo in the contract and that everything is legal? I want someone to explain what I don't understand.
Does the agent list their clients on their web site? I like to see who this person represents. I want to know who is associated with that person. I may want to ask them a question.
As I draw nearer to the agent game, I am thinking more about these questions. I want an agent that will work with me and do the best for me. I want one who is concerned about me as a person. I want someone I can talk to and they will listen.