As we learned on yesterday’s daf the Sages conclude from the pasuk in Vayikra (25:14) – which is the source for the prohibition of ona’a – that ona’a applies only when something is sold or bought me-yad amitekhah – from your fellow’s hand. Thus we conclude that ona’a does not apply in a number of cases, including the purchase of slaves, contracts, real estate and things consecrated to the Temple. The Gemara assumes that this means that purchase or sale differential of these things can be greater than one-sixth, and still the purchase or sale is valid.
Our Gemara offers a different perspective, at least in the case of hekdeshot – things that have been consecrated to the Temple – by quoting Rav Hisda who believes that by saying ona’a does not apply the Mishna means that the normal rules of ona’a does not apply, rather even more stringent rules of ona’a apply. In the case of hekdeshot, Rav Hisda rules that even a minimal difference between the actual price and the price that is paid will invalidate the sale.
Several explanations are offered for Rav Hisda’s position. The Ra’avad suggests that since the Torah is very scrupulous about evaluating the worth of consecrated objects, we cannot allow even a small overpayment to be made by the Temple. According to the Rosh, in ordinary cases, less than one-sixth overpayment is not considered ona’a because the owner “forgives” such a small error. With regard to property owned by the Temple, however, there is no one in a position to “forgive” a small overcharge, so even a small amount would be considered ona’a.