It's hard to turn down an agent who actually wants to rep you, but think carefully. My experience may offer a cautionary tale. For my first nonfiction book, I was so overjoyed to find someone who'd take it that I asked few questions, and all of them sounded paranoid the moment they left my mouth. So, feeling stupid and hoping for a quick sale, I trusted him, blind. He sold that book, yes, and my second--reluctantly--and I'll always be grateful for that. He even reworked my proposal, which many agents won't do.
But he refused to intervene with my publisher during a dispute even though he acknowledged that I was right; I did it myself and won my case. Nor did he push foreign rights aggressively; once, I got a better deal only because I insisted on making a counteroffer, against his advice. He seemed to have the attitude that I should take any offer anyone put on the table because I didn't deserve more, and never, ever did he say, after a discouraging rejection, "Hang in there. You've got a good book."
So now that I'm looking for an agent for my fiction, I'm desperate for someone, anyone, to say, "Sure, I'll take you on." But I also know what I want: an agent who won't simply submit to six editors and call it a day if they turn down my book; an agent who'll be willing to say, "Chin up"; an agent who's got enough confidence in my work to decline the first offer if it's unsuitable; an agent who'll push every foreign-rights button he or she knows. . . . That agent is a dream, and I don't know whether such a person exists. At least for me, because I'm getting discouraged.
But by all means, do your research. AgentQuery is an excellent place to start, the best I've seen, particularly because of the titles-sold listing, which gives you a glimmer of what they might be looking for.