The first one (a XP Pro SP2 OEM version) was sent back to eBay, and they quickly verified it was a fake. So the second time (less than a month apart), they didn't even question me, I'm a highly rated buyer on eBay (100% rating, 71 transactions, all were paid as soon as I won). Out of those 71 transactions, only 2 bad apples.
I've bought more duds from local merchants than that, and there's no telling how many times that I had to return clothes that in some way or the other, wouldn't fit my wife. Even had to exchange a couple of pairs of shoes that didn't fit me right.
I've had better luck on eBay. Even this notebook that I'm about to get my money back on, wasn't a bad deal. The warranty cost me $46 for two years. Shipping, even returning it, is free. So when it's all said and done, I'll have used a notebook for two years for $46. I had two others to go the same way, the first, I used a year and a half for around $40, the second, a year for $24. Go rent one and see what it costs. If you buy a warranty, chances are you'll get your money back, and use the product a long time before it breaks.