Volume license

It sounds to good to be true.

Almost certainly not, and you should post the listing so one of the little Microsoft monkeys running around here can pass it on to the proper people.

A volume license would be for people who all work for a single organization. It's not so some enterprising Craigslist scammer can buy, or get his/her hands on a copy, and then resell it to people. It might well have activated, and passed all the Windows "Genuine Advantage" (I still have yet to figure out how the word genuine fits into that name, or what the advantage is) checks, but it would have been an illegal copy none the less. And odds are, sooner or later someone (if not you) would turn the moron in after getting the volume key, and Microsoft would nuke it. Meaning they would add that license key to a blacklist, and then you would stop passing the WGA checks.

So, while I don't really consider civil "infractions" to be illegal per se, let's just say that you would be violating the terms of the license agreement and could potentially be sued by Microsoft for it. Odds are they wouldn't sue you, but they could.