In scholarly or research work, how is the credibility of the writing usually proven?

To determine the credibility of an academic writing one has to take some steps, this include:
1. Checking the credentials and the affiliations of the writer from the written paper. This will allows you to know if the author has an authority by means of his qualifications to write on a particular topic.
2. Checking out the other papers that the author has written in related topic.
3. Ensuring that the work is plagiarism free by checking to see if the work was properly peer reviewed.
4. Checking the sources that the author used in his work to see if all sources are properly referenced.

The rest don't make sense so i say the first one.