A point of sale system includes a merchant terminal and a customer terminal. The merchant terminal is configured to display a user interface (UI) window on the merchant terminal. The UI window on the merchant terminal displays a merchant-specific version of a screen displayed on the customer terminal. The merchant terminal receives updates from the customer terminal regarding the status of the payment portion for a transaction. The merchant terminal can provide an input to the UI window which is sent as a message to the customer terminal. Control of state for the point of sale system is shared such that when the system is in a first state, the merchant terminal is the state control terminal, and when the point of sale system is in a second state, the customer terminal is the state control terminal and has control of state for the system.