Stores often test stock, especially on high priced items that are both a big inventory sitting there, along with wanting to sell working units. They also often will include a local power cord for those that come with a non compatible lead ( like you buy a unit with a IEC power lead that is UK pattern but you live in a country where the lead is Schuko or Aus or US pattern), and often will include things that might not be standard for some items, like accessory kits, a soft case or even better leads than the supplied ones. The test is just so they know with some certainty the unit when sold was complete, powered on and passed basic function checks. Thus you get a pack that has been opened and resealed with the dealer tape.
Generally places will sell you demo stock, returned and tested equipment and display stock at a discount, as this has been used and no longer fits the definition as in law of "new". This should be reflected in the sale and the price.
Like a demo model car, which might have sat on the showroom floor for 3 months but which can be classed as "new", or which might have had 100km put on the clock during the normal new car delivery kilometers ( a new car can still arrive with a few hundred kilometers on the clock, from being delivered to the dealership/s and to the customer, though a new car is also only registered to the dealership/s only, never a customer registration and return, those are defined as used vehicles, even if it has no extra kilometers on the clock) but is still covered by the full warranty from manufacturer and dealership.
I have gotten some nice stuff at a very good discount that way, buying demo stuff and returns ( Thanks Toploser, they work great) and getting stuff that works like new but which is still great value.