Ah, the dreaded query letter. The truth is, it requires a different skill set and the ability to step back from your own work to write an effective query letter for an agent. A good letter that accurately represents your manuscript is highly likely to get you a response—provided you’ve done your research and you know that the agent you’re querying represents work like yours.
Before I will take on a client at the querying stage, though, I ask to read your first three chapters (which are the ones most likely to be requested with or after your query) to ensure that you’re ready to go out and compete in a rough marketplace. If I suggest you do more work on the manuscript first, I will not charge you for that review.
Why do I ask for those chapters? There are no guarantees in publishing, but if you’re serious about trying to get a contract with an agent and a mainstream publisher, you have to go in with a manuscript that stands up to scrutiny when it comes to quality and marketability. There are no shortcuts. Only then does it make sense to put the time and energy into the three rounds of feedback on your query letter.