If it were an OEM version, MAYBE... But they claim to be a Microsoft certified reseller, so ask them to provide an ID or something that you can use to verify that with Microsoft.
If they are on the up and up, they should have no problem giving you that info. If they get defensive, hostile, belligerent, try and change the subject, or basically do anything but give you some info needed to verify that they are indeed what they claim, then they're trying to scam people.