Short answers, pulled from the story.
Bargaining and haggling refer to the same process: a negotiation between a buyer and seller over the price or nature of a transaction. The terms are interchangeable, with "dickering" also used to describe the same activity.
Bargaining is most common in street markets, bazaars, and lower-income regions where centralized price regulation is difficult. In North America, Australia, and Europe it is largely confined to expensive items like automobiles, antiques, jewelry, and real estate, while in Indonesia and much of Asia it extends to everyday goods and services.
In 1950, Nash defined a classical bargaining problem as a set of joint utility allocations, with one point representing what players get if they fail to reach agreement. The Nash bargaining solution is the allocation that maximizes the product of the players' utilities across all possible agreements in the bargaining set.
Integrative bargaining, also called interest-based or win-win bargaining, is a strategy where parties collaborate to find mutually beneficial outcomes based on underlying interests rather than fixed positions. It requires multiple issues to be in play so that trade-offs across issues can create joint value for both sides.
In Southeast Asia, food is regarded as a common necessity rather than a tradable good, so negotiating its price is seen as disrespectful. Haggling for food items is strongly discouraged across the region.
Growth in a country's GDP per capita income tends to reduce both the negative effects associated with bargaining and the unscrupulous practices found in street-market settings. This helps explain why fixed-price retail has displaced haggling in wealthier economies.