Reuven exchanges a needle for a gold necklace. The necklace is worth 100 times more. Does ona'ah apply?
Barter of goods-for-goods (as opposed to produce-for-produce) is exempt from ona'ah. The willingness to trade proves the party preferred the item he received.
Question 2
A seller says: 'This article is worth only 1 zuz but I am selling it for 100 zuz; you have no ona'ah claim.' Does ona'ah apply?
When the seller explicitly discloses the actual value and the exact overcharge, and the purchaser proceeds with full knowledge, the ona'ah is waived. Financial conditions agreed to by both parties are binding.
Question 3
A court sells orphans' land worth 100 zuz for 200 zuz. Can the purchaser retract based on ona'ah?
The rule is: 'The legal power of an ordinary individual should not be greater than that of orphans.' Since land is exempt from ona'ah for ordinary transactions, a purchaser of orphans' land also cannot retract on those grounds.
Question 4
Hiring a worker to build a wall — does ona'ah apply to the wages?
Hiring a worker is treated in halacha as purchasing him for a set time, and since servants are exempt from ona'ah, no ona'ah applies to wages paid to workers.
Question 5
A person rents an animal for a week, paying six zuz when the fair price is only five. Can the owner reclaim the one-zuz overcharge from the renter months later?
Rental of objects and animals is treated as a daily sale, so ona'ah applies. Uniquely for rentals, the overcharge may be reclaimed even after a long period of time — unlike sales, there is no standard time limit.