I would be interested in other peoples opinions as to guidelines.
Here is my opinion.
1.Explain what category of Folk music, e.g, Traditional American, Contemporary English Self composed in a traditional style, or whatever.
2. Mention instrumentation.

4.Give people information in an objective way as you possibly can .
5. Do not agree to do a review, if you have a personal dislike of the artist.

7. When you have written the review, put yourself in the position of the person who you are reviewing,and imagine how it must feel, to have your music rubbished.
Colin Randall agrees on these points, ok
so we have some guidelines from a professional reviewer.