"I cannot give you the formula for success, but I can give you the formula for failure--which is: Try to please everybody."
~Herbert Bayard Swope~
Wise words to heed in any area of your life. As a writer, this is something to remember.
Some writers get caught up in entering contests, lovingly known as contest junkies. Judges comments can very greatly. Why? Because it is hard to keep personal preference from weighing in on the numbers. I remember a particularly nasty comment from a judge which put an end to my contest days. Most judges were fair and gave wonderful feedback and comments to help me. But one just made nasty comments throughout. The coordinator told me to disregard the comments, because the judge was obviously having a bad day. They dropped that score, but the comments still stung.
Along the writing path, you will submit your work to critique partners, advance readers, editors, agents, and friends. My advice to you is to remember you can't please everyone. If you try, you'll fail.
Don't rewrite your story to please another person, not even to gain a contract. Remember, this is your story. Remain true to what you want to say. That doesn't mean you shouldn't polish it, or make changes to better your work. But don't "reinvent the wheel" (pun alert!)
However, if everyone is telling you that your character is unbelievable or cardboard, then you'd better look at that character. That isn't changing your story.
Keep writing, and remember...you can't please everyone!