When you start collecting books like this, it rapidly becomes apparent that it is hard to tell where the "respectable" books leave off and the "dirty" books begin. Even the mainstream publishers were never shy about putting a titillating cover on a book if it might sell a few extra copies. Collectors nonetheless make a distinction between mainstream books that have a little sex as an extra ingredient (or pretend to) and those that have sex as their main focus (or pretend to.)
Click on the thumbnail graphic to bring up a larger (70-100K) .gif of any book's cover.
This book, Pure Sweet Hell by Malcolm Douglas (Gold Medal #972, (c) 1957, second printing) is certainly not subtle in its presentation, but it is nonetheless a "respectable" book, a crime novel having a prostitute as a central character but not really having any sexual content. The publisher, Gold Medal, pioneered the idea of publishing original stories in paperback form, rather than reprinting books previously published in hardback, and is today known as "Fawcett." Gold Medal published many now-famous authors for the first time, but was also not above publishing books such as The Lustful Ape, and, more than some publishing houses, was not totally averse to pushing the line between "reading for adults" and "adults only."
Sin Tryst by Neal Serian (Compass Line Novels #129, (c) 1966), on the other hand, leaves little room for speculation as to what kind of book it is. It has no plot to speak of, is poorly written and proofread (the people doing the proofreading didn't even notice that the name of the company is misspelled on the front cover as "Campass"). A person reading it today, however, cannot help but notice that the book itself is full of sexual teasing, heavy breathing and much ogling of breasts, but actually has a single sex scene just two paragraphs long -- much less sexual content than many of today's bestsellers.
Shakedown Street, by Louis Malley (Avon #T-394, (c) 1953) is, again, a "vintage paperback." Avon, the publisher, was one of the first paperback book publishers and remains one of the most prominent. The cover features the two things most dear to paperback publishers -- a nearly naked woman and people beating the crap out of each other -- but is a crime novel wherein the possibility of sex is always in the air but never quite happens. People really do, however, beat the crap out of each other.
Here we have Matador of Shame ( Evening Reader #1204 (c) 1965) by John Dexter (this is a pseudonym, but I'm not sure whether it was one person or a "house name," used by different members of the publisher's stable of writers). This book is a little more complicated than the others. It tells the story of the convoluted interactions between a disgraced bullfighter, his icy English wife, a movie producer, his wife, a reporter, and sundry smaller characters. The publisher of this book is well-known as a "smut" producer, and certainly the cover makes it look like the most abject trash. When one reads it, however, one finds that sex scenes are quite tame and occupy only a small portion of the text. A typical "sex scene" for a book of this vintage devotes a whole lot of attention to the female partner's breasts and then proceeds to this:
"Conchita ignited like a short-fused bundle of explosives. He knew it when her nails sank into his back. When her hips began to convulse and her feet began to pummel him. Her arms became windmills, her hips began to rock. She leaned her head all the way back and shouted all the sweet endearments she knew, and she knew some good ones."
The sex is, in other words, completely unexplicit. The rest of the book being devoted to the love, hatred, betrayals, threats of violence and violent acts between characters and between characters and bulls, and so forth. In other words, it is really more of a romance than anything else. I suspect that this book, along with many other books that appear to be smut at first glance, started as an attempt at an adventure/romance or some other "legitimate" book and, when it went unsold as such, the author put in a few mildly hot passages and sold it to Evening Reader.
The point of all of this is that the packaging of these books does not necessarily give one much of an idea of what lies beneath the cover. You will never know what is under the rock unless you turn it over.