John Walsh: The odd thing was, you never really wanted the third book

It was widely believed by authors (though seldom admitted by publishers) that the three-for-two choice of books on Waterstone's tables was not a marketing ploy by the booksellers; that in fact it was all arranged by the publishers, who paid a fee to Waterstone's to have their authors' works prominently displayed with stickers and razzmatazz.

Authors had mixed feelings. Yes, it was good to be part of a pile-'em-high promotion – it felt as if your book was heading straight for the bestseller lists. No, because it didn't exactly make you feel very special to think your book might be the third choice, selected only to make up the numbers and purchased for precisely £0.00.

For readers, there was a mystery about the three-for-two deal, as mysterious in its way as Fermat's Last Theorem. No matter what mood you were in when you entered a Waterstone's, no matter what the time of year – Christmas, spring, the onset of summer holidays – it was always weirdly hard to choose the third book. Choosing two was easy – this novel, that crime thriller – but selecting a third never worked. You looked at seven possibilities before finally settling for the title you least didn't want.

Back home, it remained by your bed for months, unread and somehow unreadable, like the runtish third pet you'd been forced to buy at Battersea Dogs Home, along with the matching dachshunds, and now couldn't be arsed to feed. A lot of readers will be glad to see the back of them.