A crimson-robed man bangs out pop songs on his piano while proclaiming, "Doesn't that sound amazing?" So begins the siren call of Stephen Ridley's piano course ads, which pop up across YouTube and beyond. He tantalizes viewers with the idea that for just $1,400, his "revolutionary" Ridley method can transform tone-deaf amateurs into virtuoso pianists able to dazzle any audience. But an investigati

