" Bandcamp is perhaps the most helpful as it does allow the artist to describe their own music and also to suggest their own "sounds like" comparisons."

Yeah, I find Bandcamp's "traditional folk" tag does seem to, by and large, feature traditional folk (rather than singer-songwriter stuff), largely cos it's artist-applied.

You can tag yourself however you like, and I think more Bandcamp artists should go a bit further in this regard: if you're a traditional singer, for instance, who plays concertina and guitar and is heavily influenced by John Kirkpatrick and Martin Carthy, then you should give yourself searchable tags like "traditional folk", "English folk", "trad", "concertina", "Martin Carthy", "John Kirkpatrick", "morris", "Child Ballads", "murder ballads" or whatever. That way, people like me, with tastes like mine, are more likely to find and buy your music.