Do the latest steps – like the Fox Trot, and that "Square Dance" that's sweeping the Louisiana Purchase!

To grasp the level of fear and insecurity that must have gripped the average purchaser of these mags in those days, note the assurance on the coupon: the book will be shipped n a plain wrapper. No worries that your postman will know that you secretly want to dance.

"Learn to dance in 5 days or pay nothing" implies that if you do learn to dance in 5 days, you pay everything. So I'm guessing there's some soul-signing-away going on here.