Okay, just a hypothetical... I am not in this position, but I imagine I could be one day.
You wrote a book and you're not thrilled with how it turned out. Your agent, however, thinks it's marketable and she can sell it. Would you want it out there in the litosphere with your name on it if you didn't LOVE it?
NOTE: After reading some of the comments, I just want to clarify. In this hypothetical, the story is not CRAP and you do not HATE it. Other people may love it... perhaps your beta readers, critique partners, etc, but you don't love it.