Outside the school, a person stood selling waterproof knapsacks. A sign above him read: “SALE! Only $100 for a knapsack!”

Mr. Wasser passed by and was interested in the knapsacks, but was concerned about the price.

“The price seems high,” he said.

“Oh, no,” replied the salesman. “I’ve seen them sold for $120, even $140.”

“Okay, I’ll take one for my son,” said Mr. Wasser. He took out $100 and purchased a knapsack.

Two days later, Mr. Wasser happened to stop in the local Costco. He saw the exact same knapsack being sold for $60. He asked whether this was a special price.

“No,” replied a salesperson, “this is the regular price.”

On the way home, Mr. Wasser stopped off at another store and saw the knapsack offered for $70. Another store sold it for $55. A small, old-time store was the most expensive at $80.

“I was gypped by the salesman outside the school,” Mr. Wasser told his wife. “This is a classic case of onaah (overcharging), grounds to invalidate the sale.”

“Then return the knapsack to him,” she said.

Mr. Wasser returned to the salesman. “Overcharging by a sixth above the going price range is a violation of onaah,” he said. “More than a sixth invalidates the sale. The highest price in the area for the knapsack is only $80, and many stores were less. I’d like my money back (C.M. 227:4).”

“Had you returned the knapsack yesterday, there would have been something to discuss,” said the salesman. “However, now it’s too late! Sorry.”

“What’s the difference?” said Mr. Wasser. “You overcharged me. It’s not like I waited a week. I just realized today that you overcharged me. You’re required to take it back. Here, ask Rabbi Dayan.”

Mr. Wasser dialed Rabbi Dayan and turned on the speakerphone.

“Someone sold me a knapsack two days ago for $100. I found out today that the very same knapsack runs between $55 and $80 in stores. Must he take it back?”

“Although significant overcharging is reason to invalidate a sale, Chazal limited the ability of people to undo sales after time passed,” replied Rabbi Dayan. “If enough time passed for the customer to verify the price and he did not do so, we presume that he was mochel — willing to forgo his claim (C.M. 227:7; Sefer Hachinuch #337; Aruch Hashulchan 227:8).”

“What is the time frame?” asked Mr. Wasser.

“This varies according to circumstances,” answered Rabbi Dayan. “The Gemara (B.M. 49b) uses the expression ‘time to show a merchant or relative.’ If the item is readily available and can easily be checked in other stores, the time would be short — possibly even the same day. Thus, since two days passed, you forfeited the right to demand restitution. Had the item been a specialty one that requires professional evaluation, the time would be longer to afford the opportunity to meet with a specialist (see C.M. 227:17).”

“What if the customer was unable to verify the price immediately?” asked Mr. Wasser. “Let’s say an emergency arose shortly after the purchase, and he had to run to the hospital?”

“He would be able to submit a claim after the emergency was over,” replied Rabbi Dayan. “Some allow him only a short time afterward; others say that once he was unable to check promptly, he can claim even a long time afterward (see Sma 227:17; Taz 227:8).”

“Even after time passed, does the seller not have at least a moral obligation to accept the item back?” asked Mr. Wasser.

“The Sma (227:31) indicates that there is not even a moral obligation after this time,” added Rabbi Dayan. “However, some authorities write that there is a moral obligation, especially if the buyer was completely unaware that he was being overcharged (see C.M. 227:17; Aruch Hashulchan 227:18).

“I should add, though,” concluded Rabbi Dayan, “that if the purchase had been from a store with a defined return policy, those terms would apply.”