It is a minefield, the art business world. When there is desire, there are those out there who are quick to take advantage of the naive or foolish.
Self-styled publishers and literary agents (as well as a gamut of book “doctors” and editors seek to take such advantage, and most 
often in varying degrees. Some are not intentionally bad people or even looking to take an artist to the cleaners; they most often are not as important or skillful or influential as they claim to be. They too look for someone to help them become greater and grander than they are.
The worst story I’ve heard was a literary agent taking the proceeds from his client and running off to Jamaica (or Aruba – I forget where), never to be heard of again, an extremely rare instance. There was also the story of Mavis Gallant too, who suffered an unscrupulous literary agent: http://www.newyorker.com/online/blogs/books/2012/07/mavis-gallants-double-dealing-literary-agent.html.
I’ve had 3 literary agents. The first agent (GEM, Darla Pfenninger) I discovered through word-of-mouth via a colleague in a local critique group. I was skeptical this agent’s prowess and ability because she claimed to be always working on a pending sale, but didn’t sport any sales record. She also didn’t disclose references from her stable – and since I was just hungry to get anyone to represent me, I never asked for any. I had heard that some professional agents will charge typical office administrative fees (for copying, mailing, and long distance phone calls and such), so the clause in the contract that demanded $150/year didn’t worry me too much. However, the mere fact I was unable to contact her should have been the first warning sign that something was amiss. After a year, my suspicions got the best of me, and I withdrew from her stable. Did GEM take me for a ride? Yes and no. The agent probably didn’t make any cash or profit from me from my measly office admin fees, but I do contend that Ms. Pfenninger probably didn’t do much to sell me.
My second agent, Monique Raphel High (Writehigh), is/was a bestselling author with many contacts who had decided to pursue a literary agent career. I had discovered her on the far-encompassing literary market website Everyone Who Is Anyone by fellow author Gerard Jones (Ginny Good) http://everyonewhosanyone.com/. I’ve kept up a good friendship with Monique over the years, even though I felt she had impatiently closed her stable far too early in her gambit. She was an excellent editor and book coach, but did not possess, I believe, the fire to be the influential and tough-as-nails agent I felt I needed. After we had garnered a near-sale with Simon & Schuster for my novel, Dark Running (http://www.amazon.com/Dark-Running-ebook/dp/B004KZOPR0/ref=sr_1_1?s=books&ie=UTF8&qid=1358106878&sr=1-1&keywords=dark+running), Monique dropped the agency. This is the only critique I would have of her; she is truly a caring soul, but she had, I believe, bitten off more than she could chew in establishing her literary agency.
Monique worked for me even after the dissolution of Writehigh. She was open to editorial work and revisions, and referred me to my third literary agent, Cherry Wiener. Cherry is a professional agent with a strong track record of sales to large houses; she has had in her stable a variety of authors with varying genres, however, after spending a year with her, I discovered our personalities did not mesh well. I had felt strongly that even though she was a pro, Cherry did very little for my works or for me. I contend that this close business relationship between an agent and an author should not be based upon the agent “shotgunning” proposals without care if the manuscript would sell or not. I felt that she took me on as an afterthought, and if I sold somewhere, then she would give me the time of day. She would argue that I was too impatient, and even though I felt there is merit with that, I still don’t think she really cared for my works. So, Cherry and I split without much ado in November, 2010.
Yet, the argument here is that a good literary agent who knows well the markets and upholds a strong book of contacts, is the best path to monetary publishing success in the literary world sans the self-publishing endeavor that many new and amateur authors are given to do these days.
Yet, for any author who has yet to break the barrier in getting his/her first book deal with a major house, even having a good and influential literary agent doesn’t mean a sale, and there are bad ones out there who will charge you upfront for fees and expenses for their services and front for editors to professionally work over your manuscript. One case in point came to me from the bestselling author, Steve Alten, (Meg) who confided to me some years ago that his literary agent at AEI milked him first before cutting out extra fees after-the-sale. Dean R. Koontz disclosed to me once that he disliked a certain agency so intensely, he actively lobbied against their business all the time. So, what to do to get not only AN agent, but a GOOD agent?
And don’t be afraid to ask the agent what qualifications they have!
Thanks for the top tips. Best of Luck