Why does John Nye violate the law of one price?

John’s new book War, Wine, and Taxes sells new for $29.95 on Amazon [TC: this is correcting a previous mistake in listing the price], with free shipping in the U.S.  Many of the used copies of John’s book are selling for over $30, others in the $25-30 range, and the shipping charges are higher than Amazon’s.  Last I looked, none of the forty used copies were selling for less than $25 and one was selling for $50.

It is not hard to get a new copy of John’s book, John assures me.  What’s up?