“What if the customer was unable to verify the price until later?” asked Mr. Wasser. “Let’s say an emergency arose shortly after the purchase, and he had to run to the hospital?”
“In that case, he would be able to submit a claim after the emergency was over,” replied Rabbi Dayan. “Some say he has only a short time after the emergency. Others say once he does not have the ability to check promptly, he can claim even a long time afterward.” (See SM”A 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 SM”A [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. Furthermore, if the customer used the item after finding out that he was overcharged, he forfeits his rights to undo the sale.” (Nesivos 232:1; Aruch Hashulchan 227:8)