Many of the pilgrims in the General Prologue are trying to appear to be something they're not. The Prioress wants to appear to be a courtly dilettante. The Merchant would like people to think he's financially solvent. The narrator helps us see through these deceptions, and they become part of what makes The Canterbury Tales funny. Other pilgrims make their living through deception; like the Pardoner, who makes a pretty penny on fake relics, or the Friar, who convinces people he's poor enough to deserve charity. Still other characters portray powerless social groups, like women and the elderly, as particularly likely to engage in deception. This accusation reveals the way people in power can keep that power by calling into question the very words the powerless speak. But perhaps the most important way in which lies and deceit make their appearance in The Canterbury Tales is in their association with tale-telling. This raises the question of what makes a story true, and of how the categories of truth and falsehood apply to literature, if at all.
In the General Prologue to The Canterbury Tales, it's impossible to separate appearances from reality.
Although The Canterbury Tales portray deception as a vice that irreparably hurts oneself and others, they also make the point that almost everyone engages in it every day.