Older than you. Never mind. Your cryptic reply seemed to imply that you knew something not obvious. Like how keys are procured that actually work but aren't official.
I very much doubt you are unless you're in your 50s. Gray market keys from a plethora of methods. None of which can be discussed on this forum because it's piracy. That is why I'm being cryptic.
For the record and this is where I will be less cryptic, there is no such thing as a fake key. There are unfortunately a lot of workarounds to trick just about anything into believing it's a legitimate copy and still gain updates. This goes for cheap software up to software that costs thousands upon thousands of dollars that needs a USB dongle to work. Those are bypassed with ease.
There is absolutely nothing that can stand in the way of unscrupulous parties.
Now, aside from that, gray market websites use stolen card info to buy up keys and sell them for cheap, except it never cost them a dime. Eventually those keys will be axed as the software company learns of this act. And then there's legitimate keys that get isolated from a pool of authenticated keys that get sold off. This last one is harder to track. Near impossible even for a company like Microsoft.
The big difference with sites like that and authorized resellers is the latter buys up blocks of keys or serials if you will to resell at a slightly discounted cost because they got a larger discount buying in bulk from a developer/company.
Drop me a PM if you want me to give you the birds and the bees talk.