Prices are worldwide very different.
While US$ 29.90 is for a 404 page non-fiction book in the US a common price, somebody in India would expect less than the half price.
I have many contacts to publishers in poorer countries. I want to motivate them to sell my book in the Englisch version in their country.
But this should be with a lower price.
But since there are search engines, somebody could fast find out in a rich country, that the book is cheaper some where else.
So I would like to propose vocher codes or prices set to specific countries and that the shoping systems verifies the IP to be from such a country.