Polish your manuscript as best as you can, then get a couple beta readers or an editor to read for problems.
Don't say anything back to them, don't defend or explain. Just thank them. If they hurt your feelings, get over it as quickly as you can, then look to see how valid their feedback is. Tweak the work according to what you see as valid feedback.
Remember, this book isn't you it's Your Work. Your Intellectual Property. You wrote it, you own it. You can lease it out a hundred times, a hundred ways, but never Ever sell all your rights for length of copyright.