Why are journalist always skeptical about using materials from public relations practitioners with

principles of public relations

They have different motives. Not all meet the standard but a good journalist should explore all sides and present a fact based explaination of the truth. P.R. people on the other hand, are paid to manage the public image of people, organizations and businesses and most often present a very one-sided view.

A journalist may take into consideration the materials but using that information alone would fall far below the standard of good journalism.