Most of the books that I own go no further back than the 1960s in terms of paperbacks so I was surprised to discover after buying a 1942 copy of Russian Fables by Ivan Krylov that in the old days Penguin used to sell adverts on the inside front cover, inside back and on the outside back cover. Presumably readers in those days knew what they liked and did not require some dust jacket blurb to entice them. Mind you quite what the relationship is between Russian stories and torches is anyone's guess. This advert for Mazda colied-coil lamps is printed on the back cover.
