 The proposals considered so far invoke considerations of pre-institutional morality and/or rationality. But the ethics of surplus sharing might instead be traced to established customs. Macneil (1986) suggests that markets give rise to complex norms of “gift-giving” in commercial exchange. These gift-giving norms encourage agents to refrain from claiming as much of the surplus as possible and have an important role to play in maintaining social bonds, especially in contexts where constant haggling undermines trust and creates impediments to contracting. For example, sellers of antiques will offer discounts to those who reveal their enthusiastic interest in purchasing an item. By rewarding disclosures against self-interest, the sellers promote solidarity and cooperation in the market for antiques. Macneil observes that norms of gift-giving are more likely to emerge where the cooperative surplus is large and repeat interaction generates high interdependence.