What is the difference between buying on the basis of a purchase, and bidding on the basis of a bid?

Question:
He says: Honorable Shaykh, may Allah grant you success, what is the difference between buying on the basis of a purchase and bidding on the basis of a bid?

Answer:
The difference is clear. One person comes to buy a commodity, and you tell him, "You are being cheated; return it and sell it to me for less than that." This is buying. No, this is selling on the basis of a sale. Buying on the basis of a purchase: a person comes and buys a commodity from someone. He buys a commodity from someone, and you go to the seller and say, "The one who bought from you is cheating you. I will buy it from you for more than what he paid, so cancel the sale and give it to me." This is buying on the basis of a purchase. Yes.