Have you ever read a book that was so full of mistakes you just wanted to throw it down? Have you quit reading a story just because you couldn't wade through all of the mistakes in it to simply enjoy the story? I have experienced both of these things.
Perhaps you think that you could never write something that was full of mistakes. Maybe you think your writing would be perfect and not have a single mistake in it, but you are wrong. If you are human, you will make mistakes no matter how learned in the English language you are and no matter how much of an expert on grammar, punctuation, and spelling you believe yourself to be.
If you want to satisfy and entertain your reader so much that he/she will buy more of your books or read more of your stories, then you need to hire an editor to clean up all of the mistakes you made while writing your story.
What will an editor do for you?
An editor will do more than proofread your work. An editor will point out holes that you may have left in the plot, and places where you messed up on things like the names of your characters. No, the editor won't be telling you that you named your character wrong, but will point out if you accidentally called your character by the wrong name.
An editor will point out if more needs to be added to the story, or if parts need to be taken out. I like to give things away far too soon. My editor points out to me where I do this so I can fix it.
An editor will point out any grammatical mistakes you may have made. Using modifiers properly seems to be a big problem There are misplaced modifiers, squinty modifiers, and dangling modifiers. Then there is subject/verb agreement, as well as issues with verbs.
Spelling your words correctly is very important, as is using the correct word. Consistently misspelled words will make your reader think that you just haven't taken much care in writing your story. Mixed-up homonyms and/or words can be funny, but they also show that you didn't have your work proofed and edited.
If commas, semi-colons, colons, periods, exclamation points, dashes, or hyphens are used in the wrong way, the meaning of your sentence could be changed completely from what you intended. The meaning could be hilarious, or the meaning could be detrimental to your story. An editor would point this out to you.
It can be confusing knowing just when to begin a new paragraph, but your editor can help you with this. It is confusing for your reader when a new paragraph isn't started for each new speaker, or each switch in time and/or location.
If your sentences tend to be awkward or clumsy, your editor will make suggestions on how your sentences could be written better. Don't be so touchy about your writing that this offends you. Your editor is only doing his/her job and trying to make your writing flow.
Your editor wants your work to do well. He/she has put a lot of work into your story. A good editor will be friendly and not talk down to you. A good editor will also try and help you learn from your mistakes. Is he/she trying to work his/her way out of future jobs? No, but future jobs will not be as difficult if you learn from your mistakes.
An editor does cost money, but hiring a good one may be crucial to the success of your book. You won't be guaranteed success, but your chances of succeeding will be greatly improved.