I recently upgraded my PC and laptop and in doing so I had to move my copy of MS Office 2010 to the new machines. I bought this almost two years ago from a dealer on eBay. It had validated and registered OK when first installed so I did not anticipate any problems.
Imagine my surprise when it was flagged up as a bad serial number. I contacted MS about this and they referred me to their "how to tell" [microsoft.com
...] website. This confirmed that my copy was indeed counterfeit. I contacted the "lady" who had sold this to me as I still had the receipt. After exchanging several emails it became clear that she was not interested in giving me a refund. This was despite me proving conclusively that I had bought it from her.
I then gave up and decided to follow the procedure set out on the MS website. This involved parcelling up the offending software and sending it to them along with proof of purchase. They then further confirmed that it was counterfeit and informed me that I was entitled to a "complimentary kit", which was basically a replacement copy. This was delivered two or three weeks later. Good job!
Useful tip if this ever happens to you. ;)