As the "Subject" suggests could Doghouse include/displays the "Purchase at:" field. This becomes very relevant if your Format is ePub/eBook. It then makes if very easy for those searching for eBooks to know where they can purchase that book; Apple iBooks, Amazon Kindle, Kobo, ebook.com, Google Play, Hive, etc
EDIT: just realised this idea would also apply across all the pedia's as we can now legally download; DVD's, Books, CD,s & Games. e.g. A DVD can be purchase from; Apple iTunes, Google Prime etc. All this sourcing info would be a great help to searches of Doghouse.