Keep in mind, too, that Chaucer tells us repeatedly that he is not so smart or that he is only reporting what he sees. Don't believe it! Chaucer is very clever and is using both direct and indirect characterization to tell you about his pilgrims.
The Pardoner is supposed to be serving the people of the country. However, he is deceiving them by using relics he KNOWS are false and conning them out of their hard-earned money. The Pardoner rides in the BACK, indicating he trusts no one...since he's bringing up the rear and able to keep an eye on all the others. He keeps company with the Summoner...another winner. The Pardoner also drinks and womanizes. Chaucer is telling us that this guy, among so many others from the church, is no one you want to know. In fact, Chaucer only truly approves of three pilgrims...the knight, the parson, and the plowman.