In twenty years behind the till in The Bookshop, Wigtown, Shaun Bythell has met pretty much every kind of customer there is - from the charming, erudite and deep-pocketed to the eccentric, flatulent and possibly larcenous. In Seven Kinds of People You Find in Bookshops he distils the essence of his experience into a warm, witty and quirky taxonomy of the book-loving public.