Earlier this year Amazon sparked a book price-war by upping its discount on NYT bestsellers. Last week, in just under two hours, Bol.com gave away 20,000 books at a cost of more than £100,000. In return, it got 40,000 book buyers to register their e-mail addresses, and lengthy articles in at least two national newspapers. In terms of marketing spend it was a cheap deal. How can internet booksellers afford to undercut their prices? Six online booksellers talk about their strategies. – The Bookseller