Mishnayos Kesuvos Perek 11 Mishnah 5

The halakha with regard to the assessment of the judges of the value of a piece of property in order to sell it is as follows: Where they decreased the price by one-sixth of its market value or added one-sixth to its market value, their sale is void. Rabban Shimon ben Gamliel says: Their sale is valid. If it were so that the sale is void, then what advantage is there to the power of the court over an ordinary person? However, if they made a document of inspection, i.e., an announcement that people should come to inspect the field and bid on the property, then even if they sold property worth one hundred dinars for two hundred dinars, or sold property worth two hundred dinars for one hundred dinars, their sale is valid, as the transaction was agreed upon and done publicly.

שׁוּם הַדַּיָּנִין שֶׁפִּחֲתוּ שְׁתוּת אוֹ הוֹסִיפוּ שְׁתוּת, מִכְרָן בָּטֵל. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, מִכְרָן קַיָּם. אִם כֵּן מַה כֹּחַ בֵּית דִּין יָפֶה. אֲבָל אִם עָשׂוּ אִגֶּרֶת בִּקֹּרֶת, אֲפִלּוּ מָכְרוּ שָׁוֶה מָנֶה בְּמָאתַיִם, אוֹ שָׁוֶה מָאתַיִם בְּמָנֶה, מִכְרָן קַיָּם: