Everything is in the shader nodes that exist in the Material Room.  Most freebies are set up with the most minimal number of shaders simply to just dress the character.  No effort is put into further development.  However, more elaborate characters will have better shader node construct which will impart realistic responses to scene lighting.  But, because there are significant variations between Poser versions, you will find various shader application to deal with shortcomings of the applications. 

If you are interested in rendering realistic skin textures irregardless of which model/character and skin texture is available, I would strongly recommend Bagginsbill's VSSProp.  It is a script utility which can apply shader noeds across several material zones with the click of a button.  And it also has a built in skin shader template which is far more superior than any skin shader available anywhere.