It's selling accounts people aren't supposed to sell.

Some of the windows keys like this are Volume license sales, VLK. Some of the office ones are .EDU administrators that aren't real or are crooked.

Like a person might have administrator access to an Office 365 for an education domain where they can just create as many clients as they need or want and they'll sell an account filled in with generated user profile data. That account might be banned in a month or it'll run forever for no cost. Total gamble that is pretty much entirely determined by how blatant the seller is. Technically illegal. Basically an everyday occurrence no one bats an eye at. They just hand it bans to the most obvious sellers.

Edu accounts get 5 PCs with nearly every application office 365 has to offer.