2.3 Competitive Market Equilibrium

Every market transaction involves a buyer (the party seeking to purchase), a seller (the party offering the good for sale), and an agreed price (the specific amount both parties consent to). The transaction does not require a physical location — it can occur virtually.

In this scenario, the student who posted the ticket online is the seller — they are offering the ticket for sale. The student who purchases the ticket is the buyer — they are seeking to acquire the good. The agreed price is whatever amount both students mutually accept to complete the trade.

The social media platform is merely the mechanism that connects buyer and seller — it is not a buyer or seller itself. Labelling the buyer as the seller or vice versa inverts the roles entirely. The face value printed on the ticket is irrelevant unless both parties agree to trade at exactly that amount.

The correct answer identifies the purchasing student as the buyer, the posting student as the seller, and the mutually accepted amount as the agreed price — matching all three definitional elements precisely.

The question asks which option correctly assigns all three roles: buyer, seller, and agreed price in a peer-to-peer online ticket transaction.

The first option reverses the roles of buyer and seller — it labels the posting (selling) student as the buyer and the purchasing student as the seller. This is definitionally incorrect.

The third option names the social media platform as the seller, and the fourth names it as the buyer. In reality the platform merely facilitates contact; it neither purchases nor sells the ticket. Both options are incorrect.

The second option correctly assigns the purchasing student as buyer, the posting student as seller, and the mutually agreed transaction amount as the agreed price — all three elements are accurately identified.

Consumer sovereignty is the principle that consumers, through their free and voluntary purchasing decisions, ultimately determine what is bought and sold. No buyer is compelled to purchase any good — each weighs the price against their own willingness to pay and decides independently.

When the bakery raises its price to $7,somecustomersjudgethattheloafisnotworth$7 to them personally. They stop buying — not because they are forced to, but because the price now exceeds what they individually value the product at. This is precisely consumer sovereignty: voluntary, preference-driven choice.

Producer surplus concerns the gain to sellers from selling above their minimum acceptable price — it is not about buyers stopping purchases. Allocative efficiency requires MB = MC at the market level, which is not what is being described here. Market equilibrium refers to $Q_d=Q_s$, not to individual purchasing decisions.

The scenario specifically shows buyers freely withdrawing from the market when price rises above their personal valuation — the defining feature of consumer sovereignty.

The question asks which principle is best illustrated when individual customers stop buying after a price increase because the good no longer matches their personal valuation.

Producer surplus measures the benefit to the bakery (seller), not the behaviour of buyers who choose to leave the market. Since the question focuses on buyer decisions, this option is irrelevant.

Allocative efficiency requires a comparison of marginal benefit and marginal cost across the whole market — no such comparison is made here. Market equilibrium requires $Q_d=Q_s$; the scenario describes individual customers stopping purchases, not the market-wide balance of quantities.

Only consumer sovereignty directly captures the idea that buyers freely decide, based on personal valuation, whether to purchase at the going price — which is exactly what the departing customers are doing.