Or if they used the same standard shopping protocol, that anyone could implement or use (like they use e-mail for communication with customers almost universally). You'd add your favorite e-shop URL to your favorite desktop shopping app, and you'd see products from various shops in one interface.
The app could have customer centric functionality, since it would be a "user agent". So you'd have stuff like price tracking, availability tracking, feature comparison, independent reviews, saveable shopping cart, global wishlist, consistent user interface that never changes unless you want it to, and is configurable by you, etc.
Seller would implement the protocol for their side and buyers would choose UI app to discover and order stuff, be it CLI or GUI, or scripted.