A decent but lengthy start to reading about fakesong is the ESPB itself. Reading, as I have frequently, Child's headnotes to each ballad, you can't escape from the fact that Child heavily criticised, occasionally with sacrcasm, many of the versions, particularly in the first 3 volumes. (For some reason after that he suddenly went silent...I have my suspicions why), particularly the overegged versions of Peter Buchan.

If you want a very short summary, just before he died, see p182 in vol.5, his parting shot.