We are probably in a case where prediction markets are useless, since nobody but the author knows. However, the prediction markets could be of help in aggregating leaked information —but the time window for this (if any) is very narrow, prior to the official launch of the book.
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© NewsFutures
Harry Potter will survive The Deathly Hallows.
DISCLOSURE: The (totally uninformed) author of this blog post is long on the Harry Potter survival. 
What of the publishers, the printers; the distributors; the merchandisers etc……loads of people will know the outcome by now….hence the reason that the traditional bookmakers shut their book on the event, and are now offering a market on who performed the killing. This information should be made available to the uninformed traders on Newsfutures;
http://www.news.com.au/adelaidenow/story/0,22606,21865354-5006343,00.html
You’re right…
1. People in the show-business are used to keep secrets. Hollywood’s dream factories know that the secrecy about plots are the foundation of their business.
2. The people coming betting on William Hill could be second-hand insiders… or it could be that there was a rumor circulating among fans… and that the NewsFutures speculators were sound enough not to swallow it.
My own opinion is that the insiders have no reason to trade on Newsfutures (they are not interested in the notion of bragging rights). Moreover, it is extremely unlikely that they are even aware of the prediction exchange.
They are interested however, in being able to take 500 sterling of William Hill, on a failrly anonymous basis. And this it would seem is what they have indeed done.
The fact that the newsfutures market has not fallen into line, gives rise to the notion that it represents nothing more than an amalgam of uninformed guessers, who are ignorant in the psychology of traditional betting markets.
If Harry Potter is killed off; there will certainly be a lot of explaining to do……
It’s probable that you are right.
However, you’re a bit too harsh on NewsFutures. Usually, it works quite well, relatively. This Harry Potter prediction market is particular because there is not much public information to aggregate.
The future will tell us whether this William Hill speculative bubble was meaningful or meaningless.
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THE FATE OF HARRY POTTER IN J.K. ROWLING’S 7TH BOOK, THE DEATHLY HALLOWS: prediction market vs. bookmaker
http://www.midasoracle.org/2007/07/23/the-fate-of-harry-potter-in-jk-rowlings-7th-book-the-deathly-hallows-prediction-market-vs-bookmaker/