Recently I had a set of headphones fail after ~1 year and all I had to do was find the item in my order history click a button, answer a few questions and in this case they just credited the amount to my account, didn't even have to send them back. Instructions told me to recycle them.
There is a certain amount of trust in the system.
However it can also go wrong. Once I sent a GPU for repair because a fan stopped working and it was still under warranty. Sadly they or their repair center marked it as a no fix, recycled the card and I was credited the amount I paid, sadly that was during the GPU crunch and a card that had similar performance was not available for even close that price. Replacing a fan I could have done my self but I thought a warranty claim would be the correct thing to do incase something else breaks.