By Michael Neff
First of all, should you trust the advice of just any literary agent when it comes to editing or "fixing" your novel-in-progress? Would you trust a mechanic to fix your car if you knew he had never touched an engine in his life and could only quote passages from an instructional manual? Of course not. You would be foolish!
Yet many writers do just that.
Experienced agents with good reputations do understand what makes a novel sell, and their advice on how to prepare a manuscript for the commercial fiction market should be obeyed. However, when it comes to the nuances and process of actual fiction writing and story structuring, most agents can only guess or repeat what they've heard from others. As a writer, you must approach with caution, compare and contrast what you hear from various sources before making a crucial decision that could either save your novel or damn it for eternity.
If you are fortunate enough to have the ear of an agent who also has a solid background in fiction writing (like an Eve Bridburg or a Peter Rubie), then breathe a bit easier. If he or she tells you to rewrite X or Y to get Z, then YOU DO IT!
And btw, whatever you do, DO NOT EXCLUSIVELY RELY on your parents, friends, or writer group for advice. They are amateurs--well meaning, yes, but still amateurs.
Your best advice, on both a macro and micro level, will come from professional writer/editors with years of experience in the literary biz, i.e., individuals who understand the commercial book market, who have actively edited fiction writing, worked one-on-one with fiction writers, as well as created their own fiction--whether in the form of short stories or novels.