It doesn't watch the shelf. It answers from the inventory count you import — a CSV export or a webhook from whatever you already ring sales on. A confident yes needs a count fresher than your freshness window. Given one: five or more on hand gets "yes, we have that." One to four: "we've got a couple left, let me get someone to confirm." Zero: "we don't carry that right now."
A fresh count is the entire basis of the yes, and it is never a live feed of your shelf. That is the trade we made on purpose: an answer you can stand behind beats an answer that is quick.