Some of it has to do with differences in the way the shading engines work between Poser (for which DAZ content is built) and Carrara. Bump values are calculated globally (with reference to the world coordinates) in one, and locally in the other. Likewise, there's a different engine for calculating highlights between the two.

Converting between the two shading systems is problematic at best. I don't know anyone who's satisfied with the conversion, but there's no good way to create a universal importer that will work on all content.

A lot of DAZ content has the same shader information repeated for multiple material zones, too, which you may want to consolidate. For example, when I import Victoria 4.2, I get 29 shaders. If I tell Carrara to consolidate duplicates, that gets reduced to 14.

Might be nice if they added some controls that would let us, individually, add conversion values for shaders (like, always reduce bump to 5% of the imported value) because no two people are going to use the same values.

The best thing to do, I've found, is to bring your content in, tweak the shaders, then save the content back as a Carrara file, and use that file in the future.