Let’s say your agent has sold your book for you. Once the contract is done there is a changing of the guard from agent to editor as the editorial process proceeds.
Most agents will stay out of the way at this point, asking only to be cc’d on correspondence and only getting involved if there is a major bashing of heads. But on occasion agents do involve themselves in this part of the editorial process, most often to the detriment of the book. The way I’ve seen it manifest is that an author will complain about the editor’s editorial requests and the agent will act as an enabler for the author’s discontent.
I don’t suggest that my clients should always agree with an editor’s opinion, but I do think they should carefully and rationally consider it, and in some cases at least attempt to revise in accordance with the editor’s requests. Often times the author will discover that the changes do make sense after they begin them.
So now the book is done, and this is where I’ve seen and experienced other problems. The editor has developed this close bond with the author, and so they start conveying information and decisions about the book’s publication without speaking to the agent. Cover art is selected and catalog copy written. Information about print runs, pricing, and other logistical details is shared. Or perhaps later the publisher decides not to release a paperback edition or lets the book go out of print.
In my opinion, and in the opinion of almost every agent I know, these are all details that need to be shared and discussed with the agent, often in advance of speaking to the author. Our advice to our client in such situations is part of the fifteen percent we earn, especially in the case of a debut author who knows little about such details.
An example. Cover art is one of the most contentious issues between authors, agents, and editors. The art is typically generated by the publisher, and then most editors share the cover art with the author as either a courtesy or because of contractual obligation. Few authors actually have approval over cover art, but most contracts should state that you have a legal right to be consulted.
I’ve heard of some editors who present cover art to authors without hinting that the author’s opinion is either desired or matters, and a debut author may not feel comfortable speaking up. This corresponds with the commonly held view on the publisher's side of things that such decisions are best made by publishers. However, I absolutely feel that authors should provide their input on such decisions, though delicately, and so it’s important to have an agent there to avoid any land mines.
I actually know of a few very good editors who simply just don’t get why the agent should be involved in such conversations. As a result, I always suggest to writers to make sure to involve your agent in everything and tell your editor to do the same. Make your agent earn their fifteen percent.