Transaction interface control

A merchant point-of-sale (POS) system used in performing POS transactions between a customer and a merchant, the point of sale system comprising:

• a customer terminal configured to display a customer POS interface, the customer POS interface configured to receive input from the customer during a POS transaction with the merchant;
• a merchant terminal configured to display a merchant POS interface, the merchant POS interface configured to receive input from the merchant during the POS transaction with the customer;
• one or more processors;
• and
• one or more non-transitory computer-readable media storing instructions executable by the one or more processors, wherein the instructions program the one or more processors to perform acts comprising:
• receiving, at the customer terminal via the customer POS interface, a first input, the first input comprising customer data;
• sending, from the customer terminal to the merchant terminal, an indication of the first input;
• responsive to the indication of the first input, activating a locked mode of the merchant POS interface, wherein the locked mode substantially precludes data input by the merchant on the merchant POS interface;
• receiving, at the customer terminal, an indication of completion of the first input;
• sending, from the customer terminal to the merchant terminal, a message indicating completion of the first input;
• and
• responsive to the message, de-activating the locked mode of the merchant POS interface.