My story: The artwork arrived on Dec 24th. Seriously, I skipped Christmas and New Year's Eve before I opened the file. To be honest, I did provide detailed backgrounds on both of my main characters and luckily, they looked awesome!
The Second peek: Okay, now you are calm. You are examining your characters' faces and clothes, actions, etc. You accept the illustrator's creativity, he or she did a great job, but a few of the pictures bother you.
Advice: Re-read your story paragraph by paragraph and you can find slips--the wrong color or a missing item in the background. Is there a direct reference in the story? Or did you expect the readers to infer setting details and actions from your writing?
The Final look: My publisher provided a draft with highlighted passages, indicting the location of illustrations. I matched each passage with a picture and commented on mistakes, which stood out. Also, I found an extra picture and realized that I had misinterpreted a final picture in the story.
Finally, I wrote the publisher about my discoveries. Now I must wait and see.