The only way to know is to try me. If it needs work and I want to represent it, I'll tell you. If I choose not to agent you, you should know that I'm not judging you or your writing, or even your idea. I am saying that it's just not right for me. Some of the genres I generally will not represent include thrillers, westerns, romances, occult, science fiction, children's and young adult.
Author fleshes out idea.
I recommend beginning with table of contents or outline. Fiction author writes book. Agent will respond favorably and request your proposal or manuscript or will respond negatively. Keep good records of who responds. If the agent decides to represent you, he or she will call you or meet you to make sure there is some chemistry and explain guidelines.