The crucial elements are understanding of the music they're reviewing, the ability to write, and a firm editor. Money in itself isn't a factor, although a professional journalist should at least be able to write.

If you want reviewers to be paid, you won't get many reviews - most folk journals don't have enough resources.

Folk magazines have a lot in common with folk clubs. Many are run on a shoestring by enthusiasts who may have little or no prior experience.   Reviewers are like floor singers, some are very good and others are not. In many cases editors are simply glad to get enough copy to fill the magazine, just as a club organiser is glad to get enough singers to fill the evening.

It must be frustrating for a professional to have so many aspects of their livelihood in the hands of well-meaning but not necessarily competent amateurs, but that's the nature of the folk scene.