[londons_explore]

I suspect that in the past stores had more staff and more different departments, which were each smaller. Think more like market stalls. Each department might not have staff dedicated to payments, but instead roving salespeople designed to advertise the benefits of goods, and then to complete the sale there and then on the shop floor.

These salespeople probably weren't paid well, or identified well, so the shipowner couldn't trust them. Instead, for every payment, they need to get a receipt from a central place, which prevents any dishonesty.