Supermarket app

Supermarket A produces an app such that enables customers shopping at any other supermarket to scan the items (or perhaps the till receipt) when shopping at any other store. The app the calculates to price difference to shopping at Supermarket A and gives a discount (potentially an amount related to the difference) which can be claimed from a future shop at supermarket A.

The advantage to the supermarket is the data and the discount incentive to shop with them. The advantage to the customer is the discount.