In my experience, the chances of getting something counterfeit on eBay is higher than it is on Amazon. I had an issue where I bought a blu ray on eBay to save a couple bucks; the product the arrived was clearly a pirated BD-R. Another time, I bought a couple of batteries for my laptop on eBay; the batteries were clearly counterfeit and of inferior construction than the more expensive original batteries.

I have never had experiences like that with Amazon, but I have read stories on the internet. I believe Amazon making it easier to leave negative feedback than eBay is one reason this kind of nonsense is less common on Amazon.