Sayyiduna Abdullah bin Umar (may Allah be pleased with them) narrated that the Messenger of Allah (peace and blessings be upon him) said: No person should interfere in the buying and selling of his brother.

Sayyiduna Abu Huraira (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: Do not go out to meet (trade) caravans (with the intention of buying their goods before they reach the city). No one should sell over the sale of his brother, and no one should practice najsh (artificially inflating prices), and no townsman should sell for a villager, and do not tie up the udders of goats (to deceive buyers by making them appear full of milk). But if someone buys an animal in this (last) situation, then after milking it, he has two options: if he is satisfied with the sale, he may keep the animal, and if he is not satisfied, he may return it along with a sa’ (measure) of dates.

Sayyiduna Abu Hurairah (may Allah be pleased with him) narrated that the Noble Messenger (peace and blessings of Allah be upon him) forbade intercepting (trading) caravans, and that a townsman should not sell goods on behalf of a villager, and that a woman should not stipulate the divorce of her (religious or blood-related) sister, and that one should not bid against his brother’s bid. Likewise, he forbade najsh (artificially inflating prices) and tasriyah (concealing defects in goods).