The invention relates to a transaction method between a customer and a service terminal (4) forming part of a plurality of service terminals that supply in situ pay products and/or services selected by the customer. The invention also relates to a selling system for implementing said transaction method. An order voucher (6) comprising an identification (62) of the service terminal (4) is transmitted to a services central office (3) via a mobile radiotelephone network (2) by means of a portable mobile device (1) of the customer. The creditworthiness of the customer who transmitted the order voucher (6) is then checked by the services central office (3). In case of positive creditworthiness, said central office sends a credit voucher comprising a credit value via a communication network (2') to the service terminal (4) defined by the service terminal identification (62). The service terminal (4) authorizes the selection of a product and/or service on the basis of the credit voucher it received and supplies the desired product or service in line with the selection made by the customer. The service terminal sends a delivery confirmation comprising an amount due for the delivered product or service to the services central office (3), which then debits said amount due from an account of the customer.