What the old man is selling Austen is quite obviously a poison which Austen will use to kill his wife. The old man never says explicitly what the substance is. This is understandable, since he would not want to be an accessory to murder. The old man doesn't say it is a glove cleaner or a life cleaner. He probably suggests that Austen might call it a glove cleaner if his wife happened to find it and asked him about it. Also, Austen might want to be able to explain what it is if the police happened to find it while investigating his wife's death. What the old man does tell Austen is that it is undetectable. The victim wouldn't be able to smell it or taste it in food or drink, and a coroner wouldn't be able to detect it in an autopsy. This is what makes it so expensive. "The Chaser" is supposed to be a funny story, not to be taken seriously. John Collier wrote several stories in which a man murders his wife. He was not suggesting that men really ought to do it. He had a macabre sense of humor and a wild imagination.