Some canards I've gleaned down the years:

It ain't folk if we know who wrote it

Folk can't be about cars, motorbikes, pension schemes or computers

Any apparently cheerful folk song ends with someone's death

It ain't folk if we learn it from sheet music

It ain't folk if it has a drum kit in it

Folk rock is just rock and roll with a fiddle in it

You can turn any song into a folk song by unplugging everything and singing it down your nose

It can't be folk if you're singing it poshly dressed

I'll get me (scruffy) coat...