The shop owns what is being sold — products, forms of them, brands, stock, pictures, reviews. Commerce owns the money — one basket, one payment, one invoice. They are separate because the basket has to be able to hold a product, a promoted advertisement and an invoice at the same time and take one payment for all three.

A catalogue with no prices is a showroom, and the platform treats it as one: an item with no price says "ask about the price" and offers no button. Nothing has to be switched on for that.

The basket, then where it is going and by which carrier, then the address, then payment. A basket of things that do not ship has three steps instead of four, and only the last step ever submits an order.