"The Wandering Tellurian" is a 1967 novel by Alan Schwartz, published as one half of an Ace Double.
The book takes place in some undefined far future space opera, where guilds of people on advanced worlds sell arms to planets that have slipped back into primitive conditions. The book follows one Maikal Wendel, who has just graduated from an academy and has set out to trade weapons. Apparently, Wendel doubts the wisdom and morality of the trade, instead believing in a group called "The Ecologists", but is under paternal pressure to join the family business. After a chapter in which he visits a planet that finds his mission laughable, he finds a primitive, feudal world where he attempts to sell the warring nobles gunpowder. The nobles are fighting amongst themselves, as well as conquering the gentle humanoid natives of the planet. It is a brutally violent world, and Maikal finds it distasteful, but it is part of the business for him. He also has advanced weaponry and forcefields that protect him personally, so he doesn't feel very much risk. At the end of the book, he switches to helping the native people out to fight the human settlers, gets paid with a ship full of tobacco, and flies home, with neither him nor the reader much the wiser.
As far as Ace Doubles go, this book was notably more violent, less moral, and seemed to have a much less formed backstory than others I have read. Like other Ace Doubles, it involves a highly advanced space traveller landing on a feudal world: a way to mix sword and sorcery together with high technology, fitting two genres in one hundred pages.
What was also interesting about this book for me is that this is the only book that Alan Schwartz wrote for Ace, and indeed, seems to be his only published work. Resources such as the Science Fiction Encyclopedia only have a line about this book under his biography. Ace Doubles featured many authors that were either famous (or would become famous), or who were at least well known journeyman writers in the science-fiction world. But Alan Schwartz has no biographical information about him online. One source lists this book and another book, written in 1980, called "No Country for Old Men", (which is not the much more famous book by Cormac McCarthy) as being by the same Alan Schwartz, but given the gap in publishing years, the difference in genre (that was a spy thriller), and lack of any collaborative biographical information, that seems likely to be an error. Neither is the Alan Schwartz who wrote this book the same as the Alan Schwartz who was the last president of Bear Stearns before it disappeared. "Alan Schwartz" is a common enough name, so there is no reason to believe the author is the same as any other person who had the name. For that matter, this being Ace, the story could be a pen name of another, more famous author.
In literary theory, there is a school of criticism called "The Death of the Author", where the author is believed to have no authority over the text: it is only how a reader receives it that matters. This theory often has to butt up against the reality that authors make extensive public explanations of their texts. But here, we have an author that is, if not literally dead, unknowable. The central problem of the book, Maikal's seemingly flat affect as he engages in the brutal business of weapons dealing, could be a political statement, from either a conservative or liberal viewpoint, it could be a note on the absurdity of life, it could be topical to the conflicts of the time, it could be a lack of skill at portraying human nature by the author, but we don't know. We don't know the age, nationality, or even gender of Alan Schwartz, what year the manuscript was written, whether it was the sole writing project of a man who is now a retired insurance executive in Connecticut, or whether this is a lost classic of Philip K Dick's, written under a pseudonym. All we have is a brief, somewhat abrupt book that seems to relate somehow to the rising cynicism of the late 1960s, but other than that, it is up for the reader to draw their own conclusions.