Whats the deal with cheap Microsoft or Adobe products?

Hey all
I’ve been searching through Gameflip app and came accross some super cheap key codes for Windows 10 or Office 2019 or Photoshop and Acrobat. All for less than 10USD
Now the original price for these products is well over 100 dollars, but how people selling them for so much less money on Gameflip? And most of those sellers are highly rated also.
But are these keys legal and legitimate?
Anyone has any experience regarding these keys?