This post is geared towards those who want to self-publish. If you are trying to traditionally publish (especially if you are trying to get an agent) I recommend that you do NOT hire a freelance editor to work on your manuscript before you submit. There are two major reason for my stance.
Agents do more than serve as a messenger to publishers. They mentor writers, negotiate contracts, secure foreign rights, and are often the only way to get a new author in front of the Big 5. Before we get into the process of obtaining an agent, it's prudent to discuss what they do.