1994 318i convertible question.

I recently picked up a 94 convertible and while the top functions properly and looks as good as new the headliner is falling out. I've found a couple of plastic pieces stitched in and was able to re-attach them to the roof frame and it helped but it's still sagging all over. The dealer referred me to a shop that could repair it. That shop told me the whole top would have to be replaced if I wanted it done right. At that point I snickered and thanked him for his time. After the fact it dawned on me that I know nothing about these tops. Could there be some truth to it?