Reviewers should be professional, representative, and diverse. They should have strong academic competence in the field to which the manuscript is submitted. For example, a Ph.D. degree. Competent reviewers must have a deep understanding of their assigned area of expertise and some review experience. They will be able to identify unnoticeable errors in a paper's dataset or detect subtle novelties. The reviewer base should be as comprehensive as possible. (Typically, each submission is reviewed by at least three reviewers or more.)
A qualified peer-reviewer typically is:
Qualified to Ph.D. level or above in the relevant area.
Possesses the necessary expertise and experience to assess the paper.
Capable of formulating an unbiased, impartial, and timely review report
Has a good publication history.