I purchased a key for Office 2021. Key had already been used by c***********@live.com to validate another installation. This suggests the key had been sold twice.
Advertised at USD39.99, but should have been legit at this price. Had to buy another one. In both cases "handling" and "Tax" were added. The review link they sent me to their site post sale expired too quickly.
In fairness the second key worked, as has Windows 11, and they do offer support to fix this (and in my case they did). But for this to happen it means I am not the only one it is happening to. They do now advise that you validate your product *within 2 hours*. Down from "30 days to redeem the key" and then "whenever" to use it. I would still recommend if you need it now, but not for the shelf or a future project.