Our Gemara on Amud Beis discusses the laws of fraudulent overcharging:
Rava said: The Halacha is that if the disparity in actual value versus amount paid is less than one-sixth, the merchandise is acquired immediately. If the disparity is greater than one-sixth, either party can demand nullification of the transaction. If the disparity is precisely one-sixth, the buyer has acquired the merchandise, and the one who benefited from the exploitation returns the sum gained by the exploitation.
This is a three-tiered system: Less than ⅙ is a small enough sum that we assume the buyer and seller forgive the difference, and neither has any further claims. More than ⅙ is too large a sum, and the entire purchase is invalidated, as it is built on a fundamental incorrect valuation. The middle case is at the point where the disparity is not more or less than ⅙. Here payment is refunded but the sale is still valid.
There is definitely something psychologically and spiritually appealing to a three-tiered system. Most matters can fit into a three-part system of classification. Too much, too little, and just right, as Goldilocks was known to say. This is beyond the Brisker “tzvey dinim “, and takes us into the territory of “three dinim”. (By the way, Rav Zevin in his biography of the Rogotchover in Ishim Veshittos, suggests that the Rogotchover used three dinim as a conceptual approach in counterpoint to Brisker methodology.)
This three tiered system can be seen as representative of a deeper truth about distortion and connection to God. (I am borrowing from ideas expressed in Likkutei Halachos, but adapting them differently, see Choshen Mishpat, Shelichus, 5:38-40, and Laws of Buying and Selling 4:19) The ⅙ mark represents the sixth day of creation, which represents a coherence of God and the physical world, accomplished by the human spirit, which was when Man came on the scene. Dishonesty and distortions which are less than a sixth, i.e. the efforts to cohere and restore the creation from its natural deficiencies and limitations (days prior to creation of man culminating in his creation) are, so to speak, forgiven and automatically part of the process. Should a person fall short of full apprehension of the truth and become misguided, since his intentions are good and he is trying to connect to God, the transaction is not nullified or useless. The distortion needs to be corrected and “paid back”, but the overall action is valid. The disparity of greater than a sixth signifies a complete rejection and usurping of the mission of creation. If a person fully breaks with God and rejects the mission to unify creation, which is represented by a disparity of more than a sixth (rejecting the sixth day), the entire action is disqualified.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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