[privateSFacct]

A factor may be availability and not wanting to overload a choice.

Let's say you are way down in list, and pop up to be the Amazon Choice. That drives real sales increases. They might look at how many in warehouse local to you. Persons A, B, C put in cart - they slow rate at which AC shows up until they get a sense of whether all those will become sales or some will expire from cart etc.

Amazon has some places that feel like they have softer consistency guarantees. Ie, something shows up, but with some time passing things like price might change even while in your cart etc.