My present agent has a manuscript of mine she couldn't sell, and the response we received is that the niche is too small. The fact that your work remains unsold doesn't mean that the agent isn't doing a good job. That agent may actually be doing an excellent job of representing you.
Here are a few questions to ask as you consider switching agents.
1. Are you receiving copies of publisher's rejection emails or letters? Generally, when an editor returns rejections by letter or email within a few weeks it's reasonable to expect copies of these rejection letters either as they come in or regularly—such as once a month. We don't like reading what the editors say about our manuscripts—but at least we can document that our agent is circulating our work. Granted that many writers have fragile egos, but an agent owes us this information, even if it's only to say, "Revell passed on your novel."
2. Does the agent pay royalties on time? Generally, within ten days after a publishing house sends a check, writers should receive the statements and a check from their agents.
3. Is your agent difficult to reach? Is she lax about returning email messages or voice messages? If you speak with your agent and explain your dissatisfaction, that conversation may resolve the issues. You probably won't be able to do it in person (the best way), so telephones are the next-best approach. Emails, faxes, and registered letters seem quite impersonal, but if you have no good communication skills you may have to resort to the impersonal.
If you consider firing your agent,
the first question to ask yourself is, "Why?"