Even when exporting to reflowable ePub the result is mostly horrendous :/
It usually happens when people who don't know how to use Adobe InDesign, design a book for someone and that book happen to come to you. Although, Adobe's conversion is not perfect regardless, if it was as simple as pressing a few buttons and getting a fixed layout ePub, ePub conversion service companies wouldn't be in business now would they?
I wrote a post here about how to turn a reflowable ePub to a fixed layout one in a few steps, it's really simple if you know basic html/css.