An open-box item is frequently identical to a new one in every way that matters, and it still sells for noticeably less. The gap is created by the rules around what may be called new, not by the state of the goods.
New has a specific meaning
A product described as new is understood to have had no prior owner and to arrive with its packaging and accessories intact.
Once a box has been opened by a customer, that claim can no longer be made honestly, regardless of whether the item was ever used.
Retailers therefore create a separate condition for such stock, and the price attached to it reflects the loss of the new description.
The retailer cannot verify what happened to it
A returned item spends time outside the retailer's control, and the return process establishes that it powers on and appears complete rather than that it is undamaged.
Missing accessories, swapped components and cosmetic marks are common enough that some risk has to be assumed on every unit.
The discount prices that residual uncertainty, which is why the reduction is larger on complex products than on simple ones.
Warranty and returns are usually shortened
Manufacturer warranty periods often run from the original purchase date rather than from the second sale, so part of the coverage may already be spent.
Retailers frequently attach shorter return windows to open-box goods, and clearance conditions sometimes remove returns entirely.
Those reduced protections are a real part of what makes the item cheaper, and they are the part most often overlooked when comparing prices.
The alternative would cost the retailer more
Holding open-box stock is expensive. It occupies space, depreciates as newer models arrive and cannot be sold through the main channel.
Returning it to the manufacturer is possible for some categories but usually recovers less than a discounted local sale.
Clearing it quickly at a reduction is the cheapest available option, which is why open-box prices fall faster than new prices on the same product.
Where the discount is worth taking
The best cases are recently returned current models bought in store, where the contents can be checked and the warranty is still substantially intact.
The weakest cases are items whose value sits in a consumable part, or older stock where the remaining warranty is short and accessories are unavailable.
Inspecting the box before paying resolves most of the uncertainty, which is the practical difference between a genuine saving and a discount that was priced correctly.