I have someone who wants to sell the full version on Window 7 Home Premium who said that he got it from somewhere that it was a returned product. The package was opened but nothing missing. How can you tell if the Activation Key has been used before. He also doesn't know if it is OEM or not. If it is OEM would it tell on the packaging and/or on the disk. The packaging looks like a retail box and not the cardboard envelope that an OEM usually comes in. He doesn't want to sell it if it isn't useful because of being activated before.