Questions: Adverse Selection and Market Equilibrium

Question 1

In a used car market, buyers cannot distinguish 'peaches' (worth $14K to sellers) from 'lemons' (worth $6K to sellers). Both types are equally common, so buyers offer $10K. What happens?

• A. Both types of sellers accept $10K and the market is stable at that price
• B. Lemon sellers accept but peach sellers exit — average quality falls, buyers lower their offer, more sellers exit, and the market unravels
• C. Peach sellers accept happily because $10K still exceeds their reservation value
• D. Buyers raise their offer to $14K to ensure peach sellers participate

Answer: (B)

This is the Akerlof unraveling mechanism. At $10K, peach sellers (whose cars are worth $14K to them) are receiving less than their good is worth — they exit. Now the market consists mostly of lemons. Buyers, knowing this, revise the average quality downward and lower their offer. More sellers exit. The self-reinforcing spiral continues because each exit by high-quality sellers worsens the average quality, justifying a lower price, which induces further exits. The market collapses toward low quality or disappears entirely — even though gains from trade exist (buyers value peaches at more than $14K).

Question 2

A car dealer offers a 2-year comprehensive warranty to signal that their cars are high quality. Why can't a lemon dealer simply copy this signal?

• A. Lemon dealers are legally prohibited from offering warranties in most jurisdictions
• B. A lemon dealer would face enormous expected repair costs under the same warranty, making mimicry unprofitable — the signal is credible precisely because it is more costly for low-quality sellers
• C. Buyers would not believe the warranty unless the dealer had an established reputation
• D. The warranty only works as a signal if it costs more than the price premium it commands

Answer: (B)

A signal is credible only if it satisfies the single-crossing property: the cost of the signal must differ across types such that low-quality types cannot profitably mimic it. A lemon dealer offering a 2-year warranty on a defective car would incur massive repair costs — far exceeding the price premium the warranty enables. A peach dealer incurs few repair costs under the same warranty. This cost asymmetry is what makes the signal credible. If warranties were cheap for everyone, they would convey no information.

Question 3

In a separating equilibrium achieved through signaling, total market surplus equals what it would be under full information, because most goods are correctly priced.

• T. True
• F. False

Answer: False

This is a key misconception. Even in a separating equilibrium, surplus is lower than the full-information benchmark. The reason is that signaling consumes real resources: education credentials require time and money, warranties create repair obligations, and screening contracts distort coverage away from first-best. These costs are pure waste — they exist only to communicate information that would be freely available under full information. The separating equilibrium prevents market collapse but does not recover the lost surplus; it merely stops the bleeding.

Question 4

Adverse selection can cause high-quality goods to exit a market even though buyers would be willing to pay for them at a price the seller would accept.

• T. True
• F. False

Answer: True

This is precisely the lemons problem. Buyers would pay $14K for a peach if they knew it was a peach, and sellers would accept $14K. The gains from trade exist. But because buyers cannot distinguish peaches from lemons, they offer only the average-quality price. This price is below what peach sellers require, so they exit — even though the trade would be mutually beneficial under full information. The information asymmetry, not a lack of value, kills the market for high-quality goods.

Question 5

Explain why separating equilibria achieved through signaling or screening still represent a welfare loss compared to full information, even though they prevent market collapse.

Model answer: In a separating equilibrium, the market avoids collapse — high and low quality trade at their correct prices. But reaching this outcome requires costly actions: high-quality sellers spend resources on signals (warranties, education) that low-quality types cannot profitably mimic, and screening contracts distort coverage away from the first-best (e.g., safe insurance customers get less coverage than they'd want under full information). These costs are deadweight losses — they exist only to transmit information that would be free under full information. Separation is better than pooling with unraveling, but worse than a world where types are observable.

The comparison is a three-way one: pooling equilibrium (possibly unstable) vs. separating equilibrium (stable but costly) vs. full-information equilibrium (costless, first-best). The separating equilibrium is a constrained optimum — the best achievable given the information problem — but the information problem itself creates real social costs. This is why information asymmetry reduces total surplus even when markets don't fully collapse.