I recently browsed to their site looking to buy 'The Travel Book' and stumbled upon the offer. I believe the offer runs for the whole January. Found the price to be cheaper than several retail bookshops I recently visited.
Terms & conditions (30% SALE)
Titles available in-stock in each country may differ. No backordering available.
Offer may not be combined with other special deals, discounts or promotions (including promotional codes).
Offer excludes pre-orders, print guide bundles (many are already discounted by 30%), the title India: Essential Encounters and delivery charges.
Terms & conditions (Free Delivery)
Free delivery offer is available on orders shipping within Australia only (excludes New Zealand, Asia and Pacific destinations).
Free delivery is no longer available on orders shipping to New Zealand.
Order total is based on discounted prices and excludes delivery charges
Excludes pre-order titles and the title India: Essential Encounters
Offer applies to standard shipping options only. Express delivery options are charged at the specified rates
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Edit: Just found that despite it's still January, they changed their sale to 45% until 22/1. Truly disappointed with their promotion run as I have purchased a couple of books on the 30% sale.
A quick search on booko show the book you were looking at slightly cheaper on "the nile" $51.29 & Ebay.
Still not a bad deal for buying direct (which is usually a lot more expensive)