Many of the MS Office for sale on eBay are not legitimate such as copies that are register under a MS account where one must log into a MS account using a provided name and password. Others are educational versions where one must be a student in order to use. Some may be part of corporate licensing which can not be legally sold and only used by employees of a corporation, etc.

Some are sold from overseas in other countries which may not be covered by US Copyright laws.

However there are methods to determine the legitimacy of a Microsoft software products such as contacting Microsoft asking them, providing them with a key, etc.

I'm uncertain about selling used copies and transferring the license to another person to be used on another PC. There are different types of licensing for Microsoft Products. I'm no expert on MS softwares and installations. However have been installing and using legally licensed Microsoft products since DOS 1.x. Before DOS I was running machines with CP/M versions 1.4 and 2.2. Typical cost of a PC back in those days was from ~$1500.00 to over ~$3,000.00. In 2018 dollars which would equate to ~$4,344.00 to over ~$8,689.00.


See Article "Copy". "Move" or "Transfer" an Office installation to another computer.

https://answers.microsoft.com/en-us/...79111d1?auth=1