For flailing book retailers, the new Harry Potter tome is like a kiss of life. Potter nerds dressed up in academic gowns and wizard hats queuing up around the block to hand over Real Cash Money. The RRP for the book is $45 (outrageous!), but you don't have to walk far to get a cheaper price. Competition is hot for the dork dollar.

It seems Big W might have taken the game a bit far. It advertised the book for $15 for one day only, with the usual `while stocks last' type qualification. According to social media some stores had only a box or two of books and sold out soon after opening on said sale day. Hell has no fury like a Potter fan robbed of a cheap read. Big W's Facebook page quickly filled with complaints. News coverage followed.

It's against the law to advertise Harry Potter books (or any other goods or services) at a particular price unless you have reasonable supplies available for a reasonable period. It's called bait advertising and it can be prosecuted as an offence under the Australian Consumer Law. The maximum penalty is $1.1M per contravention.

Whether Big W is headed for Azkaban (or at least a hefty fine) will depend on whether its supplies were reasonable having regard to the nature of the market for the Harry Potter book and the nature of the ad. A `while stocks last' type qualification isn't a strong defence. You still have to think about consumer expectations for that kind of product.

Maybe people would expect a risk of not snapping up the latest Harry Potter on day 1 of its release, especially if it's heavily discounted. But if Facebook is right (when is it wrong?), then some stores stocked less than 50 books. A risky play by Big W. The negative press and potential ACCC investigation might quickly outweigh the upside of their magical marketing tactic.