Caveat emptor—“let the buyer beware”—is not a Jewish concept.

While consumers have responsibilities to be careful in the marketplace, sellers have an equal or even greater responsibility to promote their products fairly and to represent them accurately.

The Mishnah lays the foundations for law in this area of commerce at M Bava Metzia 4:11–12. For example, we learn there that, should a person contract to buy produce from a particular field, the seller may not mix in produce from another field; this is so even if the added produce is of equivalent quality. 

However, in a case where the quality of the product in question is clearly enhanced by the substitution, such as if a wine merchant were to add stronger wine to a weaker wine, that kind of substitution is permissible.

(Later halakhic authorities limit this permission, stressing that if such a substitution is not to the satisfaction of the buyer, e.g., the taste of the wine is changed, or it affects other factors important to the buyer, the buyer can refuse the sale.)

The case of adding water to wine is more interesting.

In ancient times, wine was produced, shipped, and generally sold in concentrated form. The consumer then diluted it for use later on.

At the retail level, then, a wine merchant must provide disclosure if the wine has already been diluted, but the Mishnah prohibits selling diluted wine at the wholesale level, “since this is only done for the sake of deception” (M Bava Metzia 4:11).

This would not be the case in a locale where doing so was the regular practice of wholesalers.

The rabbis were also aware that the appearance of goods is very important to increasing sales, and were thus concerned that sellers not deceive consumers by presenting their wares in a way that was deceptive.

This is termed g’neivat ayin, which refers specifically to the act of illicitly creating an illusory effect for one’s own benefit.

(The term g’neivat ayin literally means “stealing the eye,” i.e., of the consumer.)

Examples given in the Mishnah at M Bava Metzia 4:12 include cosmetically altering the appearance of goods or even animals for the sake of making them appear healthier or younger than they really are. 

This does not mean that merchants may not enhance their products with decoration to make them more attractive, but only that they may not hide imperfections by doing so.

In another example in the Mishnah (from the same passage as above), the sage Abba Shaul prohibits a merchant from selling pounded beans that have already been sifted.

His concern is that the merchant will have two reasons to raise the price: because the beans are now being sold without their husks and stems (resulting in a higher quality product), and also in order to compensate the merchant for his effort. 

Abba Shaul thought this would make it impossible for the consumer to compare the price of this merchant’s beans with the beans of another merchant who simply sells whole beans, taking into account the presence of waste material and not having any extra labor to include in the price.

The other sages disagree and permit this practice as long as the merchant does not “steal the eye” by placing the sifted product on top and the unsifted beans below, thus creating a false impression in the mind of the consumer.

Parallel to the concept of g’neivat ayin is g’neivat da·at—fooling consumers mentally.

(The expression g’neivat da·at means literally “stealing the opinion” by creating a false impression in the mind of the consumer.)

Maimonides states in the Mishneh Torah, Hilchot Mekchirah 18:1: “It is forbidden to deceive a person in business dealings, or to fool them mentally…. If one knows that a product has a defect, it must be disclosed to the buyer. Even to deceive a consumer using [mere] words is forbidden.” 

Finding the precise line between presenting one’s wares in an attractive and positive light without crossing the line into misrepresentation is a challenge every businessperson must face.

The halakhah, however, is clear that while merchants may encourage consumers to make a particular purchase, they may in no way endeavor to deceive consumers about the quality of the goods being offered for sale.

Furthermore, Jewish law seriously constrains the ability of vendors to limit liability for defects found later.

Contracts containing broad releases from responsibility are not enforceable under Jewish law, although clauses referring to specific defects may be deemed licit (Mishneh Torah, Hilchot Mechirah 15:6).

The rationale for this is clear: at the time of purchase, buyers will normally not be overly concerned about such disclaimers on the part of merchants because consumers do not generally expect the products they purchase to be defective.

Furthermore, a seller may also not minimize the importance of a defect while disclosing it, but must allow buyers absolute freedom in determining whether or not they wish to purchase a given item by being totally frank about whatever defects the product might have (Mishneh Torah, Hilchot Mechirah 18:1).

Sellers also may not give advice to less-educated consumers that will unfairly influence them to prefer some particular product.

This is based on the biblical verse (Leviticus 19:14): “You shall not insult the deaf, or place a stumbling block before the blind. You shall fear your God: I am the Eternal.”

In today’s marketplace, consumers often shop for complex items (for example, electronics) about which they may not have enough expertise to make a fully informed decision it is important for vendors to be aware that their special expertise entails a special level of responsibility, and that they must therefore be exceptionally careful not to manipulate a consumer’s decision unfairly.

The principles described above can also be applied to certain unethical promotional activities, such as “bait and switch” advertising, in which a product available only in very small quantities is advertised at a very low price merely to lure customers to a store so that a merchant can attempt to sell a far more expensive item in its stead.

This is clearly a case of g’neivat da·at: an instance in which one’s intention is being purposefully, and unjustly, manipulated by an unscrupulous advertiser.

The Mishnah (M Bava Metzia 4:12) records an interesting disagreement between Rabbi Judah and the sages.

Rabbi Judah states that “a store owner may not distribute parched corn or nuts to children, since this accustoms them to come to that store.”

The dispute appears to involve the case of children sent on errands to local stores. Given the choice, any child will choose to enter a store with a history of giving out treats for free, and this will certainly be so regardless of the price of the goods on sale in that particular shop.

The sages disagree with Rabbi Judah’s option prohibiting giving out treats to children. These sages seeking to preserve the sense of free competition they valued in the marketplace, allowed this practice since, as the Talmud explains, other shopkeepers were always free to offer even better treats! 

The key, of course, is finding the boundary between the valid promotion of wares, on the one hand, and, on the other hand, g’neivat da·at, unfair manipulation of the consumer—which is particularly true of modern advertising and promotional techniques directed toward children. 

Modern Jews may well wish to favor Rabbi Judah’s position, which seems to reflect the idea that, when no parent is present to help direct the child’s decision responsibly, the marketplace has to be regulated to ensure that children are not artfully manipulated into wasting their parents’ money.

Additionally, there is ample halakhic justification to set standards on the promotion of products that are clearly harmful to children and adolescents, such as alcohol, tobacco, violent movies and video games, and the like.

Finally, it is clearly preferable to promote products based on their own merits rather than by disparaging the products of a competitor.

In the Palestinian Talmud (Yerushalmi Chagigah 2:1), Rabbi Yossi ben Ḥanina states, “Extolling one’s own virtues by disparaging another person causes one to lose one’s share in the World to Come.”

Translated into the world of commerce, this means that advertisers may make claims in the marketplace about the worth or superiority of specific products, but they must not do so fraudulently or in a purely negative mode (i.e., not by speaking highly of one’s own wares, but solely negatively about those of others).

In fact, concealing a competitor’s advantages may constitute g’neivat da·at no less clearly than concealing the flaws in one’s own products, insofar as both leave the consumer misinformed.

Adapted with permission from The Observant Life.