Those are not legitimate buys.
They are actually selling an old/refurb/decomissioned/broken Dell computer, and the associated software.
Direct from their description:
"To comply with the eBay policy:- "OEM, bundled, or recovery software may be listed only if it is included along with the original hardware, such as the motherboard, hard drive, or computer sold with the OEM software. - This listing includes the original decommissioned computer free of charge."
However....you are not even getting the hardware (the Dell PC) that you are actually buying. Unless you go find their warehouse and pick up some Dell box that probably does not actually work.
Again...that is not a legitimate Windows OS purchase.