Alternatively, see what iTunes calls it as a genre.

Vin Garbutt is country and western apparently, when I bought an album of his recently! Notwithstanding that some on here would say that he isn't folk, despite a long successful career entertaining folk music appreciating audiences...

Folk isn't really a genre. It encompasses too much. It is certainly prone to being a music of the people due to the mainly acoustic and therefore more easily attainable entertainment. Certain styles are folk in that they are easy to reproduce without expensive electronic props. Traditional songs and tunes fit the bill nicely.

But folk is and always will be subjective and whatever you are comfortable with calling it. The folk I play and love listening to most tends to be classed as roots these days. A sub genre if you really must take a librarian approach.