What does a literary agent do? Negotiate a great deal

Most likely you will sign their contract as is. You will be just too delighted and indebted. At best you may change a clause or two, but most writers will make no changes.

Here the agent is a great asset. The agent is not some first-time author desperate for a deal. She comes from a position of knowledge and strength. The publisher knows that the agent will be able to find deals with other interested publishers.