I've sold quite a few of these and have had very few customers come back with problems. There are a couple of things that I have noticed. I've had customers mention that the hinges can break off with use (happens often in the S5 as well). They apparently bought some cheap ones off of Amazon and they fit well. Another issue that I have run into a couple of times is more of a hardware defect. For some reason, the Z3 starts to vibrate for like 30-40 seconds, intermittently, on random apps. I've tried many different "fixes" but could not solve the issue (had to do a warranty exchange for the customer). Hopefully this doesn't happen to you!