Rav: If a person does business on condition that there will be no prohibition of overcharging, there is still a prohibition (as he has made a condition to negate a Mitzvah in the Torah).

Beraisa (R. Levi): The minimum amount that is considered overcharging is a peruta. The minimum amount to require an oath when a person admits to part of a debt is a peruta.

Question: What are the rights of the buyer in the overcharged item...?

Answer (Beraisa): R. Yehudah HaNasi says that he cannot retract the sale but he can demand back the extra money that he paid.

R. Nasan: The sale is cancelled.

Question (Kahana to Rav): In the first part of the Beraisa, the seller was underpaid, for example, he sold something worth 6 for 5. In the latter part, the buyer was overcharged, for example, he bought something worth 5 for 6. If so, in the first part, the underpayment was 1/6th; however, in the latter part, the overcharging was 1/5th?!

Answer (Rav): In the first part, it was 1/6th of the full value (known as milebar). In the latter part, it was 1/6th of the value paid (known as milego).

If he sold something worth 5 for 6...

Question: Why couldn't the seller say, "You lost one dinar. Take a dinar and maintain the sale!''?

Answer (R. Zeira): The buyer could answer, "It is dishonorable for me as people will say that ploni made a fool of me by taking too much money and then having mercy on me and returning it''.

Answer #2: He could answer, "It is dishonorable for me to wear a (plain) 5 dinar garment''.

R. Yochanan/ R. Elazar/ R. Hoshiyah: What is (another) reason that the sale is cancelled? As the buyer can say, "I knew from the beginning that the garment was only worth 5 dinars, but because I was under pressure to buy it, I paid 6 dinars for it. However, now that I am not under pressure, take back the garment and give me back my money.''

If he sold him a 5 dinar item for 6, if he did not manage to speak with him before the price rose to 7 (and now the buyer wants to keep it)...

R. Yaakov bar Idi/ R. Abahu citing R. Yochanan: (The seller can say), "Just as you would have backed out if its price would not have risen, so I am backing out now that it has risen.

Mishnah in Bava Basra: There are four cases of sellers - (Two of them are) He sold him good wheat and the buyer discovered that it was bad wheat, the buyer can back out (as the sale is certainly invalid even if he was not overcharged). If he sold him bad wheat and the buyer discovered that it was good wheat, the seller can back out.

R. Yosi bei R. Bun/ A Similar Beraisa: If they discussed an acquisition but no money changed hands, either may back out and there is no curse of 'the One who punished'.