It is simply part of the agent's job to work with the publisher and author in order to publish the book in the best conceivable way. A strong and effective cover is one of the most important parts of this process, so choosing not to involve your agent if you're unhappy with a proposed cover is literally insane.
My answer to problems with the cover, with editorial, with publicity, with anything else to do with the publisher: Call your agent, call your agent, call your agent.
Tuesday, July 10, 2007
"I Hate My Book Cover!" 4
From Simon Lipskar of Writers House: