The Mercedes-Benz Group is one of the world's most successful automotive companies. The company website provides the following information: "With Mercedes-Benz AG, we are one of the leading global suppliers of high-end passenger cars and premium vans. Mercedes-Benz Mobility AG offers financing, leasing, car subscription and car rental, fleet management, digital services for charging and payment, insurance brokerage, as well as innovative mobility services." Suppose, the Mercedes-Benz Group sends out researchers posing as actual customers to evaluate the service quality of their car dealers. Which research approach/method is employed in the given scenario?