From http://www.wikinfo.org/ which is very (very, very, ...) similar to
wikipedia (and whose articles often refer to WP as is source) the book sources (via ISBN link as can be seen on the frontpage under "Interesting new books") leave the user the decision about where to buy the book. There, four sources are given (with the resp. ISBN links): AddALL, PriceSCAN,Barnes & Noble, and - of course - Amazon.com. http://www.wikinfo.org/wiki.phtml?title=Special:Booksources&isbn=0521365... . One may arbitrarily add more sources (for those who want to have a really competitive market). Mark