The Jewish court has the ability to sell properties owned by an estate in order to pay debts owed by the individual who passed away. This includes outstanding loans, payment of the ketuba, etc. Generally speaking this was done by means of an announcement that the court has properties for sale – effectively a public auction – which would invite people to come and view the properties, establishing their value.
Under certain circumstances, such as selling to feed the widow or to arrange for her burial, a sale of estate property may take place without such an announcement. Similarly there were places where it was commonplace for the court to arrange the sale of property without such an announcement. Our Mishna discusses a case where the sale took place without such an announcement, and a significant error is made. According to the Tanna Kamma (first), if the error was a sixth of the value of the property, the sale is automatically nullified because of the law of ona’ah. According to Rabbi Shimon ben Gamliel, however, Jewish courts have the strength to effect a sale, even if the discrepancy is a sixth of the actual value of the property.
The law of ona’ah, which is based on the passage in Vayikra (25:14), is understood by the Sages to forbid overcharging or undercharging someone from the market price. As long as the discrepancy is less than one-sixth of the price, the sale stands and the excess must be returned; if the discrepancy reaches one-sixth of the price, the entire transaction is cancelled.
The Mishna continues and teaches that if an announcement of the auction was made, then even a wide discrepancy would not cancel the deal – property worth 100 can be sold for 200 or property worth 200 can be sold for 100. According to the Ramban, the Mishna mentioned these specific numbers because even in the case of an auction there are limits to the error that is acceptable, and a larger discrepancy would cancel the sale.