Deathworld by Harry Harrison, Science Fiction, Fantasy

While on a gambling trip to the casino on the planet Cassylia, he is challenged by a man named Kerk Pyrrus (who turns out to be the ambassador from the planet Pyrrus) to turn a large amount of money into an immense sum by gambling at a government-run casino. Some planet in the galaxy must -- by definition -- be the toughest, meanest, nastiest of all. If Pyrrus wasn't it . . . it was an awfully good approximation!