Bava Metzia 50 - Both the Seller and the Buyer Can't Cheat
Price fraud - overcharging by the seller or underpaying by the buyer - is prohibited . The law in any particular case depends on two factors: the amount of the fraud, and the period of time that elapses between the transaction and the time the defrauded party protests.
If the amount of price fraud is the discrepancy of less than 1/6, the sale stands and all claims are immediately waived. If the amount is exactly 1/6, the buyer can demand a refund. If the amount is more than one sixth, either party can void the sale.
The defrauded party has as much time as it takes to show the purchase to a merchant or to his relative for assessment.