Do you think Chaucer believes people are basically good, basically evil, or a mix of the two?

I honestly do not believe Chaucer's point was to prove that people are inherently good, bad, or a mixture of the two.  Much of what Chaucer wrote was satirical about the religion in Britain.  Satire is when an author "pokes" fun at serious topics such as religion and the government, etc.  Chaucer was well aware that there was much hypocrisy in the church, and this belief can be found in many of The Canterbury Tales.  For example, some of the characters in the tales hear people's sins and offer ways for them to atone for them.  Some of these characters offer this atonement for a high price.  They take bribes and gifts for their services.