I live in the US and out of hundreds (thousands?) of purchases only one or two have made me question if they were counterfeit, and even those worked well enough and I didn't return them. There may be a selection bias in the comments you read because the countless people like me never post their experience and the 0.001% who unluckily were repeatedly sold counterfeit will likely post about it.
I think HN commenters also overstate the problem. I’m in the US, use Amazon a lot, and haven’t noticed counterfeits. Maybe I’m just bad at identifying them.
I think it’s the type of issue where it would be a major problem for the producer of a specific product that got ripped off, and any customers who are fans of that product, but may never affect the average buyer.
No idea. I haven't experienced that either and I use amazon.de a lot.
I've had one item sold by Amazon as new that was clearly a fraud return, though, i.e. the item inside the product package was switched for a different model.