Products labeled as Showroom just indicate that a product can be viewed in selected shops to try out, touch and feel. This is just to demonstrate it.
The product you actually buy is brand new in the box and hasn't been opened.
The products which have been used in the shops might be sold later online as well, but those will be labeled properly as "Demo product", "Exhibiton product" or "Refurbished" and are sold a little bit cheaper. Also those are normally single items and in stock as one, as they are sold individually.
Hope this clears that one up! ;-)
The "Special Offers" version has ads from Amazon. These ads are usually present when the screensaver is active and at the bottom part of the Kindle’s homescreen.