Is it permissible for a pharmacist to buy medicine from someone who brings it from abroad at a lower price than its selling price to customers, knowing that he can buy it from the company at a lower price, and must he inform the seller of that?

The questioner is not at fault for purchasing the treatment at any price agreed upon with the seller. He is not obligated to adhere to the price set by the pharmacy or the company. What matters is the mutual consent of both parties, as the Prophet, peace and blessings be upon him, said: "Indeed, selling is by mutual consent."