Issues like this are common for any 3D application, not just Carrara, that imports shader/material schemes from other 3D packages. Usually there isn't a direct interpretation from method to method so we end up with a "best guess". 

The Carrara Lounge tut is a good starting point for understanding how shaders work. Shader design is one of the most robust and versatile capabilities in Carrara. Because of that, in my own tutorial series, it's also the largest section. 

For Poser content, after I adjust the shaders to suit Carrara, I'll simply save either the character or the shader in Carrara format so I don't have to repeat the process. Starting with Carrara 6, my Poser usage has dropped dramatically since Carrara does so much more - and  more easily too. But as long as the 3D content is created for Poser first and Carrara second, this will continue to be an issue.