Is it permissible for the buyer to stipulate to the seller that he not sell his commodity to anyone else in his city, such that the seller is obliged not to sell to any other person who wishes to buy the same commodity to sell it in the same city?

Issues concerning conditions in sales are among those about which there has been intense disagreement, both ancient and modern. The preponderant opinion (rajih) with us is the validity of conditions that do not contravene Islamic law and the obligation to fulfill them. This includes the right of exclusive agency, and what the questioner mentioned does not fall outside this ruling; thus, stipulating it is permissible, and fulfilling it is obligatory.