That's a very broad question but:
Here's my recent story of Amazon UK/EU
My cheap ASUS graphics card packed in the other day after 1 1/2 years. It has a 3 year warranty with ASUS. The product was purchased from Amazon.
I contacted ASUS who told me I had to go through the retailer and that under UK law the retailer must support this. They also gave me a number for what we call Consumer direct over here which is a public service that will tell you all your rights in these situations. I felt this was a bit strange that they'd given me this number without my asking for it.
I then contacted Amazon. Amazons representative told me that ASUS was completley wrong and they would only support the device for 12 months - END OF.
So I rang the consumer direct help line that ASUS had so kindly provided.
Sure enough Consumer Direct informed me that I was not only protected by UK Law but also European law and that Amazon had to support me for a reasonable amount of time on the product - and that the 3 year warranty with ASUS proved that I was well within the reasonable period of time. (Amazon Europe has it's HQ based in Luxembourg)
I've never had a problem with Amazon before and over time I've spent a lot of money with them - but I do feel betrayed this time as they have outright lied to me.
After researching the matter further it turns out I'm not the only one - plenty of people are running into this - and the
European Consumer Center has looked into this previously. I consider it quite bad that they as such a large company can continue to get away with this.
I was about to spend £1k on Canon EOS hardware through Amazon. This has made me think twice before clicking the one click buy button! I shall now be revisiting my local camera stores!