Answer:
low-ball technique
Explanation:
Low-ball technique is a method used to persuade buyers make a purchase by offering a product at low price to get the customer to commit. The price is then increased.
This is a method commonly used by sales people.
In the given scenario this was used by the salesman when a couple orally agrees to purchase an appliance at a special price, he tells them he misquoted the price, indicating it was only available for an out-of-stock model with fewer options.
Since the couple had made a commitment to buy the particular appliance, they still buy at the higher price.