In this note, I would like to describe how to bargain. Generally speaking, we know the meaning of the word "offer". If we want to bid on an item, we may make an offer. If we browse the ads in the newspaper, we may see a term: obo., which means the "or best offer". If the seller has already made an offer, what can we do? Well, make a counter offer! This is the only point in this note. Bargaining is an art. Unfortunately, I have no sense in it. But I still try to make an example here. Suppose I want to sell a used car for $9000. The buyer can give me an offer of $7500. If I intend to negotiate with him/her, I may make a counter offer: $8000.