Reverse service is after the product (service) is sold, the company provides customers with services to realize the use-value of the product (service). According to the above definition, which of the following is not a reverse service is. ['A car 4S shop provides customers with second-hand car valuation and transfer services.', 'An air-conditioning manufacturer provides customers with free on-site service for the life.', 'Products can be returned and exchanged free of charge within 7 days after an online store returns.', 'A telecom operator launched a preferential activity of "send phone calls to mobile phones".']