Back in the 1980s, I wrote my first novel pounding away on a typewriter in the back room of the frozen yogurt shop I owned and operated. When the manuscript was finished, I answered an ad an agent had put in the newspaper. (In hindsight, the "ad" should have been my first clue this wouldn't work.) The agent's initial response to me was that I could have been more creative choosing my pen name. (This should have been my second clue.) I wrote back assuring her that Edith Hemingway was my real name and I intended to use it. I did send her my manuscript, and she did offer me a contract, which I very excitedly signed and then waited for feedback on my novel.
The agent began sending me handouts about common mistakes new writers make (enough to fill a looseleaf notebook), and I kept waiting for specific feedback on which of those common mistakes applied to my work. Months later she asked me to make the 200 page manuscript longer, so I spent several months going through page by page and expanding the story by about 50 pages. I did not receive any feedback, except that it still wasn't long enough. Finally I said I wasn't going to do more revisions until she gave me specific suggestions on what needed to be done. After six months of hearing nothing, I received a registered letter stating that I had not followed any of her suggestions, I was unresponsive, and she was ending our business arrangement. I truly don't think she ever read any of my manuscript. Of course, I sat down and wrote a long letter back to her, stating that I was the one ending my business arrangement with her. It helped diffuse some of my anger, even though I never mailed it.
So what did I learn by this? First of all, not to jump at the first sign of interest, to do my homework before signing a contract with an agent, to find out what genres he/she represents, to find out if this person truly likes my work and if he/she has a personality that meshes with mine.
I did eventually give up on that manuscript, which is still sitting on the shelf, but I did lift an entire scene from that novel and inserted it (with changes, of course) in ROAD TO TATER HILL.