"try rereading p13"

You mean sentences such as: "Most songs which were later recorded as folk songs were not written by the singing and dancing throng, or by ploughboys, milkmaids, miners or weavers, but by professional or semi-professional urban songwriters or poets"

Well, personally I don't have any particular vested interest (ideological or otherwise) in whether this is true or false, likely or unlikely. Even from a class perspective, the professional or semi-professional urban songwriters are hardly likely to have been aristocrats; there was money to be made, but I doubt there was a huge amount of it (especially given how much broadside printers nicked each others material) – Roud describes broadside sellers as one step above beggars, so presumably the writers were essentially the urban working class (albeit perhaps more literate than most?).

But I'd point out that p.13 doesn't cite evidence, it makes statements. It sounds like there might be more back-up to such statements in the parts of the book I've not yet got to. I need to finish reading the book to see how much evidence of specific authorship there is. Evidence that moves beyond pointing out that a song appeared as street literature to evidence that that appearance was originary; evidence that the appearance on a broadside of, say, a Cutty Wren song or a pace egging song, or Six Dukes Went a Fishing means that Fred Bloggs, professional broadside writer, wrote it more or less around the same date it was printed.