It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "A town-dweller should not sell a Bedouin's goods for him."
"And do not go out to meet the caravans, and do not make false bids (najsh)."
"And none of you should propose marriage over his brother's proposal."
"And no woman should ask for the divorce of her sister in order to empty what is in her bowl, for she will receive only what has been written for her."
"And do not tie up the udders of camels and sheep for sale. Whoever buys such a sheep with tied-up udders has the choice between two options: if he returns it, he returns it with a sa' of dates."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13488