Authors are so often fixated so tightly on getting an agent they forget about all the ups and downs, the twists and turns a writer's career can take.
Look, it's likely you'll have an agent, it's likely you'll have a good relationship, at least for a time, but unlike a romance novel its UNlikely you'll stick with the same agent throughout your career.
The best agent I ever had retired. Sigh.
So, let's consider agents. What are some reasons you might want to terminate a relationship, other than simply discovering what a jerk he or she is (IF that is the case)?
Well, you might discover your agent is lazy, incompetent, or both. Hey, they're out there. Like any other profession, you find a lemon. If you send in a manuscript and don't hear back - check it out. If you hook up with an agent who raves about your books and says they'll do wonders and you hear nothing for months, check back. If you discover your so-called agent hasn't even read your work (it does happen), it's time to take a walk.
If you want to expand your career, move from one genre to another and include them both in your area of expertise but your agent tries to keep you pinned in one genre, then its costing you in the career growth department. If your agent takes forever to read a manuscript and get back to you then it's costing you time. If you get no input on how to broaden and grow your career, i.e. just stick with what you've always written, then it's costing you agan. Time to wave Bye-bye.
Maybe you have an agent who gives you loads of time and attention, but then you discoer this wonderful person whom you like and is very personable, just doesn't have the experience in the industry or the knowledge to open those doors for you. There are agents who've been around, there are new agents. Their status in that hierarchy can affect what they can accomplish. If the 'new' agent hasn't grown with you, if you've outpaced him or her and your work has gone beyond their ability to strongly represent you then, despite lovely personality attachments, it's time to move on.
Remember, the relationship between you and your agent is a business relationship. If your agent doesn't share your vision for the future of your career, if he isn't willing to expand, doesn't have enthusiasm for your work any longer or you plain just don't like him, then it's time to think about going in a different direction.
Breaking it off with an agent probably won't be easy, but if you find you need to do just that, then remember to be professional. Reread your contract and adhere to all contractual responsibilities. Don't try to cheat the agent no matter how frustrated and angry you may feel.
Don't twitter or blog about the termination you're contemplating and risk the embarassing situation of him or her finding out about it online before you handle it on a one-to-one basis. And don't blog or tweet about it after either.
Don't go badmouthing your agent all over creation. It's an interconnected profession. Badmouthing is not good. One caveat - in private, if asked, don't lie. Be objective, but don't feel you must praise that rare jerk. You don't want someone to think you left just for one certain reason, which might not apply to them, and have the asker hook up with what is a 'bad apple'. Be professional, but be honest. Then if they do it anyway, it's on their plate.
Remember too, that separating with an agent almost never means you'll never communicate with that person again. Assuming he or she sold something, you'll receive royalty statments, payments, and other professional bits and pieces over the years. It really is better if you keep a professional relationship and not let it devolve into bitterness.
If it's already bitter for some reason, still best to keep it on a professional and businesslike footing.