Large retailers rely on all sorts of psychological tricks and UI work to steer you to the most profitable transactions, some of which we have labelled Dark Patterns. Not just Amazon, not just online. All that is gone with agents. At least until they work out how to manipulate the agents as well as a person, most likely by buying control of the the popular agents before their competitors do.
If anything it seems like the agents would be easier to trick (at least right now).
Yup. Retailers sell a ton of popular goods at or below cost to attract customers knowing that they will load their cart with other high-margin items to make up for it. If you remove these upsells and other temptations then the store takes a big hit.