Originally Posted by
750XL
I've used these sellers numerous times on eBay and had no issues at all. I believe they simply recycle serial keys from old PC's
You can't just re-use an old licence key, the activation process ties the product key to the hardware that it was installed on, it wont work if you try to reuse an old key on a different computer. The key must either be an unused one or an OEM / VLK licence. These keys may well "work", I have heard many stories of people using them without problems but they are illegal pirated software and there is a high likelihood that they will stop working at some point in the future when Microsoft blacklists them. Also downloading and using software from a non legitimate source caries other risks in that it may contain viruses or malware, You pay your money and you take your choice!
EDIT: crossed with above post.