Do you know the old adage about lawyers who represent themselves? Well, the same is true of writers who depend upon themselves to find every error in their manuscript. It can't be done. Even two pairs of eyes can overlook blatant errors.
An author can hire a freelance editor to review his work. The cost of editing varies depending upon the type of edits provided. If an author has confidence that plot holes are covered, plot devices are firmly affixed, and the story presents all the elements that make it worthwhile reading, a copyedit may be all that is required. However, if the author knows the story needs structural help, a heavier edit would be required.
Another solution, one that doesn't cost any more than your time and friendshp is found in critique partnerships. Put a manuscript into the hands of five or six competent critique partners who will look at different aspects of the story, and an author has a very good chance of coming out with a novel that demands attention. The key word in the above sentence is competent.
This isn't to say that if critique partner A doesn't catch something that critique partner B has latched upon that A is less competent than B. Critique partners focus on different elements of the story. These elements are usually the ones that are their strengths, or they are weaknesses they are working to strengthen.
Competence comes in knowing the what, why, and how of grammar rules and the art of storytelling. For example, there is no value in a critique in which all forms of "to be" are highlighted and labeled passive. Competence requires an understanding that passive sentences are sometimes needed and that not all forms of "to be" are considered passive. Competence also requires a critique partner to understand the author's voice as well as a desire not to destroy that voice with their own.
Not all critique partnerships are the same. Some writers prefer to work soley on the elements of storytelling and leave the copyedits to others. However, having a critique partner who searches for the missing marks of punctuation as well as the glaring plotholes, is a great asset.
Authors should always edit their work to the best of their ability. Then the work should be turned over to a professional editor or to trusted critique partners who are not afraid to tell an author what is wrong (and right) with their manuscript.
Until next time, happy editing.