What's the packaging like from Amazon Japan for art books? box with some protection inside or a padded envelope.
From the last art book I got from play-asia is came in a box and the book was in a bubble wrap sleeve, this stopped the book getting damaged. The book does work out about £3 cheaper from Amazon, about £7-8 if they refund the import fee, which they should seen as a book is 0% VAT. I assume Amazon mark on the packaging that the item is a book.
Amazon JP generally has two types of packaging.
If its small enough to fit in a bubble mailer then it'll be a bubble mailer.
If its too big for a bubble mailer then its shrinkwrapped to cardboard, and placed in the center of a box.