• 'דינא דבר מצרא, "ועשית הישר והטוב בעיני ה'"

Rav said that if one purchases land, which was available to anyone willing to pay the government tax on it, and the land is located between properties owned by partners or brothers, he is an impudent person (for not allowing them to purchase it), but we do not remove him from the purchased land. Rav Nachman said we do remove him, but if the claim against him is only that of a בר מצרא – adjoining property owner (who wants to purchase it himself and have two properties side-by-side), we do not remove the purchaser. However, the Nehardeans said that we even remove the purchaser because of a בר מצרא, because the Torah says: ועשית הישר והטוב בעיני ה' – you shall do what is just and good in the eyes of Hashem. The Gemara then says, if the potential purchaser obtains permission from the adjoining property owner to buy the field, Ravina says: לא צריך למיקנא מיניה – he does not need to legally acquire the right from him to buy the property, because the permission granted is legally binding. The Nehardeans say the buyer must make a kinyan to render the בר מצרא’s permission binding.

• Exceptions to דינא דבר מצרא: מתנה, selling all properties, buying from or selling to an idolator

The Gemara lists several cases in which the  בר מצרא has no claim. A property given as a gift is not subject to the law of בר מצרא, but if he guarantees the gift (i.e., he commits to compensate the recipient if it is collected by his creditor), it must actually be a sale, and is subject to דינא דבר מצרא. If one sold all his properties to one person, the sale is not subject to דינא דבר מצרא, because the purchaser might not agree to buy the rest of his properties if one is absent, and the seller is not obligated to sustain a loss for the בר מצרא’s benefit. If one purchased land from an idolator, the purchase is not subject to דינא דבר מצרא, because he can tell the neighbor: ארי אברחי לך ממצרא – I chased a “lion” away from your border, and there is no greater “just and good” than that. If one sold a property to an idolator, it is not subject to דינא דבר מצרא, because עכו"ם ודאי לאו בר ועשית הישר והטוב הוא – an idolator is certainly not subject to the directive, “You shall do what is just and good.” However, we excommunicate the seller until he commits to compensate the neighbor for any losses resulting from the gentile buyer.

• Precedence between potential buyers – ex. Talmid Chochom vs. relative

The Gemara says that if one has the option of selling his field either to neighbors in his city or neighbors of a field he owns (and no one is a בר מצרא), שכיני העיר קודמין – the neighbors of his city take precedence, and it is proper for him to sell to them. שכן ותלמיד חכם - If his choice is between selling to a neighbor and a Torah scholar, תלמיד חכם קודם – the Torah scholar takes precedence. קרוב ותלמיד חכם תלמיד חכם קודם If his choice is between a relative and a Torah scholar, the Torah scholar takes precedence. The Gemara asks: שכן וקרוב מאי – if his choice is between a neighbor and a relative, what should he do? It answers based on a passuk: טוב שכן קרוב מאח רחוק – a good neighbor is better than a distant brother, so the neighbor takes precedence.

Siman – Pickpocket (קח). The pickpocket who did not do what was just and good in the eyes of Hashem, when he used the money he pickpocketed to purchase a field that a בר מצרא wanted to purchase, after the בר מצרא couldn’t stop his neighbor on the other side from giving away his field as a gift, stole a piece of paper from the pocket of the gift recipient which indicated he planned to sell the field to a talmid chochom, before selling it to a relative.