A marginal buyer and a marginal seller are those who barely stays in the market.
A marginal seller is a seller who is willing to sell his goods at a price equal to its economic cost; then he does not earn producer surplus. If the price becomes lower, the marginal seller will leave the market. For example, a marginal seller sells at a minimum selling price of two; anything lower than that will drive him out of the market.
Meanwhile, a marginal buyer is the one whose maximum buying price is just two; anything higher than that will drive him out of the market.What is a product benefits positioning approach?