Here is something that goes through my head every time…
Being an author is a strange profession, I am sure you will agree.
We spend hours writing our book/s, then reading it over and over. Every time I read it, I find something that needs changing. These changes can be either typing errors or I see the writing is weak and needs further caressing.
From my perspective, I believe that you should get it as close as you can to being right before giving it to a third party to proof read and edit. Once they have done their job… read it again! This is your baby and it needs your final approval. You know that you will be your toughest critic and will have the best understanding of the integrity of your story and characters.
If you still need changes, do it… once it is published you won’t be changing it again. This is your final product… you have to be happy with it and believe it is good enough for people to buy. Remember you will be the main sales person for your book. The better it is, the more you will believe in the book and the easier your job should be.
Happy story telling… it’s all about the tale and being able to share it with as many folks as you can!