The problem with a lot of websites like this is they often sell the same key several times, and eventually MS activation objects to this. I did this recently "for a laugh", and indeed it was a scam, and MS refused to accept it.
So although @
jimbo got lucky, there is no guarantee you will. In fact, if MS detect it, eventually his licence could get blocked as well.
I am not saying his site is not genuine but in the end, it is always questionable how they can sell them e.g. they may be selling cheaply licences obtained from 3rd World countries which are cheaper but not actually permitted to on-sell in other parts of the world.
So if you use such a site, go in with your eyes open, and be prepared to lose your money - CAVEAT EMPTOR applies.