An online shopping concierge service allows shoppers to purchase items on behalf of customers and checkout using a mobile application, circumventing traditional point-of-sale check-out systems. A customer places an order using a mobile application or website associated with the online shopping concierge service. The online shopping concierge service charges a payment instrument of the customer in the value of the selected items. The system transmits the order to a shopper, who receives an order for fulfillment on a mobile device. The shopper collects and scans items using a mobile application. The mobile application transmits an identification of the items for purchase and their total cost to the online shopping concierge service, which transmits payment to the retailer. Alternatively, the mobile application encodes an identification of the items for purchase into an encoded image, which is scanned by a cashier, allowing the shopper to complete an accelerated check-out.