Last week when I was shopping for Shabbos at the local Jewish-owned supermarket, I noticed boxes of imported kiwis marked ten shekels. I buy kiwis often for Shabbos and knew that for the last two months they and the other local stores have been selling these boxes for twenty shekels a box. I checked to see if they were especially soft and saw that everything seemed fine so I took five boxes instead of the one I originally planned to buy. I suspected that the worker in the store marked the wrong price but I knew that the government law is that even if it was a mistake, they have to give it to me at the price marked on the box. Sure enough, when I checked out they charged me the price that was written on the box. As I was getting ready to leave, I noticed that a worker was changing the price on the remaining boxes of kiwis, confirming my suspicion that there had been a mistake. I have two questions. First: Did I act improperly? Second: If I did act improperly, am I obligated to rectify the situation?
Before we answer your questions we need to clarify a basic issue.
One finds in the Gemara that the value of an item in a store is the current sale price of the item and not the amount that the store originally paid and not the store’s replacement cost. This can be seen from a Gemara (BM 99B) that discusses a porter who, due to negligence, broke a store’s barrel of wine. It is clear from the Gemara that the porter must pay the amount the store charged for barrels of wine on the day they were broken. Therefore, we can say that when you bought the kiwis for less than the price the store wanted to charge, the store lost money even if you paid more than the store paid, and certainly if it was less than what the store paid.
Based on our introduction it would seem that you violated two Torah laws.
The first law is based on the Gemara (BM 31A) that states: “One who sees flood waters that are approaching someone else’s field must set up an embankment to ensure that the flood waters will not enter.” The Gemara derives this from a pasuk that includes even a loss of land in the mitzvah of hashovas aveido (returning lost objects). Thus we see that the mitzvah of hashovas aveido includes not only the requirement to return lost objects but also requires a Jew to actively prevent a fellow Jew from suffering a loss. Therefore, when you noticed that the price was too low, you had a mitzvah of hashovas aveido to alert the staff of the store and ask if there was an error. Even if you did not buy at the wrong price, another person would buy and he would cause the store a loss. Thus, you violated the lav (negative command) and asei (positive command) that apply to one who ignores the commandment to return lost objects.
The second lav that you violated according to many opinions, is lo sa’amod al dam rei’echo-it is prohibited to stand idly by when a fellow Jew is being killed (if intervening won’t endanger the one who intervenes). The Rambam (Sefer Hamaitzvos 297) cites the Toras Cohanim that says that this lav is not limited to a victim who is being physically attacked but even includes an obligation to testify in a person’s defense. The Rambam clarifies that this applies not only when failure to testify can lead to a loss of life but even if the testimony will only prevent an incorrect monetary loss.
This ruling is cited by the poskim (See Pischei Teshuvo (CM 28, 4)) in reference to the obligation to testify in beis din. Furthermore, the Chafetz Chaim (Be’er Mayim Chaim Rechilus 9, 1) cites this obligation as the source for his ruling that if one notices that an unsuspecting person plans to partner with an untrustworthy individual he must alert the potential victim even though he will be speaking loshon hora (provided he abides by the Chafetz Chaim’s conditions). Since the Chafetz Chaim uses this halocho to derive a leniency it is obvious that he maintains that this ruling is authoritative.
Thus, your first question is answered. Rather than take advantage of the store’s mistake you had an obligation to alert the store of the error and in failing to do so you violated one mitzvas asei and two lavim.
Note that these commands that were violated do not generate an obligation to pay the store for the loss you caused. Even though the obligation to prevent a loss is included in the obligation to return a lost object, nevertheless you do not have an obligation to return or pay anything since you don’t have someone else’s object.
We do however see in the Gemara in a similar case that the real proper behavior is to compensate the store. This is not an obligation even on the level of lifnim meshuras hadin or dinei Shomayim, but just that you should not want to be one who caused someone a loss.
The source for this proper behavior is the principle of oni hemehapeich becharoro. This is described in the Gemara as a case in which R Gedal had made an agreement to purchase a field but had not yet done so. R Abba, who was unaware of this agreement, purchased the field. He should have not done so based on this principle since R Gedal was already on the verge of buying it. Even though after his purchase the law did not require R. Abba to sell or give it to R Gedal, he insisted on doing so. We see that R. Abba did not want to cause R. Gedal a loss even though he was not legally responsible for the loss in any way. To emulate R. Abba you should also seek not to cause the store a loss.
In order to answer your second question, whether you are required to return money to the store, we need to explain the issues involved and then you will have to determine the answer.
If there were no government law that required a store to charge what it says on the label even if it was marked in error, the Torah law would be that the sale is invalid. The reason is because when one pays too much or too little by more than one sixth, the sale is invalid under the laws of ono’o. Since the store charged you only half the proper price, your sale could be rendered invalid. However, whether the sale is actually rendered invalid or not depends on the wishes of the victim since (CM 227, 7-8) if the victim waives his right to invalidate the sale, the sale is valid.
Normally, (ibid) when one realizes that he was cheated, like the store owner did in your situation, and yet he doesn’t say anything, we interpret his behavior as acquiescence. However, since the Israeli law prevents the store owner from objecting, we can’t construe from his behavior that he waived his right to invalidate the sale.
Furthermore, we cannot rely on custom in the usual manner. The usual manner that we apply custom is that it automatically becomes a clause in a contract unless specified otherwise. For example, if a contract does not state that rent must be paid on the first day of the month but that is the custom, the renter is required to pay on the first of the month.
In this case, we cannot apply custom in this manner since one cannot (Makkos 3B, Sema CM 227, 38) insert a clause in a contract that the Torah’s laws of over and undercharging will not apply to this contact since that is called masne al ma shekosuv batorah-one cannot make an agreement to ignore the Torah’s laws. Such a clause is null and void.
It should also be mentioned that one cannot apply the law simply because it is the law of the land. Even though we must abide by the laws of the land, they do not supersede the Torah’s laws. (See for example Shach CM 73, 39.) When there is a specific Torah law that contravenes the law of the land, we must follow Torah law and may not violate the Torah’s law in order to abide by the law of the land.
However, the law and the subsequent custom may influence Torah law in your situation. If the victim willingly waives his right to nullify the sale, it remains valid. Since there is a law that the sticker determines the price, there are store owners who willingly forego their right to invalidate a sale. For example, many stores would not invalidate the sale because they wish to please their customers and since the law created a behavior norm that stores do not deviate from the sticker price, this type of store prefers to lose a small amount of money in order to satisfy its customers’ expectations. Also some store owners will willingly abide by the sale because they are respectful of the law of the land. Since there is nothing in Torah law that requires them to invalidate the sale, their respect for the law will cause them to adhere to the law even if it entails a small loss.
It is important to note that these are analyses based on possible attitudes of the store owner. In order to apply them it has to be determined if any of these assumptions apply to your store owner since if they do not, you owe money to the store.
In conclusion: You acted improperly in failing to inform the store of their error and in fact you did the opposite-you exploited the store’s error. Whether you now owe money to the store depends on the store owner’s true attitude. In practice, you should just ask the store owner if he wants you to pay him back the NIS 50 that he undercharged you.