Dunstan is set as a direct contrast to Godfrey. Where Godfrey is merely weak, Dunstan is completely bad. He is vain, arrogant, and selfish, as well as dishonest. Like Godfrey, he is primarily interested in what he himself wants, but he lacks any saving virtues. Dunstan suspects his own worthlessness: while he thinks what a fine person he is, he fears the opinions of others on that subject. This narcissism is put symbolically by having Dunstan take Godfrey's whip, as it gives a better appearance than his own.
Dunstan, like Eppie, is just the sort of person needed to fulfill his role. He serves as a contrast to Godfrey, as a means of relieving Silas of his gold, and as a reminder to Godfrey that truth will eventually reveal itself. When not needed, he can be conveniently removed from the story without being missed. He is an example of static characterization — he shows no development during the story and comes on the scene full-blown. However, he has a certain complexity: his repressed knowledge of his faults gives him a psychological interest that Eppie lacks.