Final answer:
An economist would refer to a shopper getting a good deal on a product as achieving consumer surplus, which means they pay less than they were willing to pay, thus gaining additional benefit.
Step-by-step explanation:
An economist would describe the situation when a shopper gets a "good deal" on a product by saying that the consumer achieved consumer surplus. Consumer surplus occurs when a consumer pays a price for a good or service that is less than the highest price they would have been willing to pay. This means that the shopper values the product more than the monetary amount paid for it, indicating they've attained a benefit above the cost incurred.
All suppliers make decisions on how much to offer for sale at various prices based on their production costs. Conversely, consumers decide what is best for them and the maximal price they're willing to pay for goods and services. Hence, finding a "good deal" suggests that the marketplace is effectively balancing these varied interests, and the consumer's payoff is the added value perceived from the transaction.