If someone is selling a “100-activation Office 365 key” for $20, they are either:

Some keys only work in the country where they were purchased.

The reviews seemed mixed, with some customers reporting success and others complaining about the product key not working or causing issues with their Office 365 account. Alex was still unsure about what to do.

: Counterfeit versions may not receive critical security patches or new feature updates. Legal & Free Alternatives