Bava Metzia 57B

דאפילו פחות מכדי אונאה חוזר.

in that even if the difference in price is less than the measure of exploitation, the exploited party may renege on the transaction. R' Yoḥanan does not accept the opinion of Rav Ḥisda and Reish Lakish does.

מיתיבי: רבית ואונאה להדיוט, ואין רבית ואונאה להקדש! מי אלימא ממתניתין דאוקימנא בתורת אונאה? הכי נמי: רבית ודין אונאה להדיוט, ואין רבית ודין אונאה להקדש.

The Talmud raises an objection to Rav Ḥisda’s opinion from a baraita: Dealings with a layman are subject to the halakhot of interest and exploitation, but dealings with consecrated property are not subject to the halakhot of interest and exploitation. The Talmud answers: Is the objection from the baraita stronger than that from the Mishnah, which was defused when we established it to be referring to the principle of exploitation, i.e., that the principle that up to 1/6th is not considered exploitation does not apply to consecrated property? So too the baraita should be understood: The halakhot of interest and the principle of exploitation apply to dealings with a layman, but the halakhot of interest and the principle of exploitation do not apply to dealings involving consecrated property.

אי הכי, היינו דקתני סיפא: זה חומר בהדיוט מבהקדש? ארבית! ליתני נמי: זה חומר בהקדש מבהדיוט, אאונאה!

The Talmud raises a difficulty: If so, is that consistent with that which is taught in the latter clause of that baraita: This is the stringency with regard to the layman, in contrast to the halakha with regard to consecrated property? According to this explanation, the halakha with regard to consecrated property is more stringent than the halakha with regard to a layman. The Talmud answers: This stringency is only in the case of interest, as it is permitted to collect interest from consecrated property. The Talmud asks: If so, let the tanna also teach: This is the stringency with regard to consecrated property, in contrast to the halakha with regard to the layman in the case of exploitation.