They are probably the same people that send out the emails from Nigeria asking for your SSN to collect your money from long lost relatives. I would bet the farm that they are pirated or all together fake keys.
I'd be more concerned that they sell the license key to another person too and when MS found that out, they suspend your license and deemed yours a fake.
Buy a legit copy, sell it to 20 people, huge profit.
They might be Microsoft TechNet subscription keys, but MS has really cut down on the amount of keys a sub buys you now in order to avoid scammers doing exactly this.
I signed up to TechNet about two years ago and for $150/year I received ten keys for pretty much every recent version of Windows, which is admittedly an excessive amount but an insane deal. They have since cut it down to two keys per version with some editions sharing keys. Kinda lame they did so but it's understandable why, and still a pretty good deal.