There are only two characters in the story who are named. The first is the protagonist, George Harris, and the second is George's girlfriend, Frizzie.
We know quite a lot about George and Frizzie, both individually and collectively. We know that George is a writer and that he is thoughtful and kind. Indeed, he's the only writer who thinks seriously about the critic's ideas at the beginning of the story, and he also, later in the story, expresses sympathy for the farmers who are exploited by the parking officer. We also know that George and Frizzie have "lived together for five years, in a narrow house near Cottesloe Beach." Their relationship is described as "comfortable." We also know that both George and Frizzie like to surf.
There are several other characters in the story who are not given names but are, instead, named according to their jobs or according to their relationships to other characters. There is "the critic," for example, and also the "parking officer," and then there is also "the passenger's surfer brother."
As regards "the critic," we know that he works for "a local paper" and that he has read "very little of [crime] fiction." We also know that, despite having not read much of that genre, he thinks there is too much violence and gore in crime fiction stories. Indeed, he invites the writers at the writers' festival to "Look at the body count... the compulsory autopsy scenes."
The "parking officer" seems to be an excessively punctilious, rather cold figure. He takes advantage of the farmers who park illegally because they are not familiar with the parking regulations in the city and he laughs about "sort[ing] them out." George notices that the parking officer has "a vindictive edge" to him.
The "passenger's surfer brother" is introduced in the later stages of the story. This character threatens George against testifying at his brother's murder trial. He tells George that "something unpleasant" might happen to him should he decide to testify. At the end of the story, George is murdered, and the "passenger's surfer brother" is the prime suspect.