Sometimes this involves some convoluted thinking, drawing ideas and applying concepts that have absolutely no surface relation to sales.
But there are other times when the fantasy or science fiction author specifically uses a sales situation or setting in their writing. My favorite example of this is Robert Heinlein's "If This Goes On--" in which his hero, a member of the revolution against the oppressive theocracy, has to go undercover as a textiles sales representative. This Heinlein tale provides Lesson #7 in my Handbook.
But I ran across another great example of sales IN science fiction the other day. I have an e-mail subscription to Daily Science Fiction (subscriptions are FREE!), and on Friday, March 13 (I know, right?), there was a story by James Van Pelt that really jumped out at me. I'm not a fan of spoilers, so I won't tell you anything, I'll let you read it for yourself. EXCEPT, I really DO have to note that the character in the story is a telemarketer for Tahoe timeshares... and I have to say-- Been there, done that. :)
Anyway, you can go to the story here, James Van Pelt's Everything's Unlikely.
And then sign up to get a daily dose of short sci-fi right in your very own in-box by visiting Daily Science Fiction.