כְּבָר בֵּאַרְנוּ שֶׁהַנּוֹשִׂא וְנוֹתִן בֶּאֱמוּנָה וְאָמַר כָּךְ וְכָךְ אֲנִי מִשְׂתַּכֵּר אֵין לוֹ הוֹנָיָה. וַאֲפִלּוּ אָמַר זֶה לָקַחְתִּי בְּסֶלַע וּבְעֶשֶׂר אֲנִי מוֹכֵר מֻתָּר. אֲבָל בֵּית דִּין חַיָּבִין לִפְסֹק הַשְּׁעָרִים וּלְהַעֲמִיד שׁוֹטְרִין לְכָךְ. וְלֹא יִהְיֶה כָּל אֶחָד וְאֶחָד מִשְׂתַּכֵּר כָּל מַה שֶּׁיִּרְצֶה אֶלָּא שְׁתוּת בִּלְבַד יִפְסְקוּ לָהֶם בִּשְׂכָרָם. וְלֹא יִשְׂתַּכֵּר הַמּוֹכֵר יֶתֶר עַל שְׁתוּת:
We have already explained that if a person buys and sells in a faithful manner, saying "This is the extent of profit that I am making," the laws of ona'ah do not apply. Even if he says: "I purchased the article for a sela, and I am selling it for ten," this is permitted. Nevertheless, the court is obligated to regulate prices and appoint officers of the law, so that people at large will not be able to reap whatever profit they desire. Instead, the court should regulate that a person should earn only a profit of a sixth. A seller should not profit more than a sixth of his investment.
