I spent a couple of hours recently kiting round second hand bookshops and charity shops. Both can be rich hunting grounds for garden books, although sometimes one can, quite inexplicably, draw a blank.
Charity shops are a bit odd in that way, some have no garden books out unless it's summer, presumably on the basis that no-one wants to know about gardening in winter. My marketing strategy would go the other way somewhat, but I assume, that theirs is tried and tested. My best ever charity shop purchase was a brand new, mint copy of the Hillier Manual of Trees and Shrubs (RRP £20) for a quid.
Anyway, whilst trolling around I saw this sign on the door of a charity shop. Now I can understand the potential dangers inherent in second-hand electrical goods, but I can't imagine why hardback books are also verboten.