[Update] What you should check closely when unboxing your HTC One.
Dent on HTC One after drop test of AndroidAuthority via cdn01.androidauthority.net
UPDATE1: Lots of Taiwanese guys pointed out in the comments that some photos are fake. You better take a grain of salt with the HTC One photos below. I advise you to check the comments section and don't miss their comments, I mean Taiwanese friends'. Their comments include some URLs and links that may give you additional information. Also, regardless of their authenticity, the photos can't be the proof that every single HTC One out there has defects, needless to say. Just like the HTC One handed to tech news sites for the purpose of review were good and fine one, you will have good and fine one in most cases. Just don't be an unlucky buyer. I don't know whether it would be one in a million case or one in a billion case but everything from mass production can't be without the one of hardware glitch. It doesn't matter it's iPhone, Galaxy or Lumia. There can't be the exception in that sense.
Update2: If you want to get the more information on this issue which is not from Taiwanese source. Visit the thread of xda-developers forum on this issue from the actual HTC One buyers. Some HTC One buyers mostly from UK report this gap issues like this. There are some more threads discussing HTC One's build quality issues with various pictures.
I came across a bunch of HTC One photos(photos are embedded far below). These pics were originated from various Taiwanese sites, I guess. (Lots of pics show Chinese characters and Taiwan is one of few countries where One is actually released.) I have never used HTC phone, but heard much about HTC's poor finish on their phones. HTC One is seemingly no exception this time.
A lot of people point out the fundamental cause from which all the problems are started. That's the combination of two bad choices. (Actually it's highly likely that they are related each other.)
1. With its externals, HTC One has the unibody structure which is defective unlike that of iPhone. Plastic was used to fill the gap between aluminum pieces in the back as well as the side. The glue seems to be used for their front speaker cover parts at top and bottom to attach those to the body. You can see how its speaker cover falls apart easily from AndroidAuthority's drop test below(@2:00).
In my opinion, HTC One's build quality is quite bad, contrary to the popular belief. (Don't get confused between build quality and build material. Also the design is a different matter.)
2. With its internals, it has poor design in electrical engineering sense which is glitch prone. Oddly, HTC One's battery is located between display and PCB board just like a sandwich or a hamburger. It's 3-layered structure. (You know breads can't conceal what's between them.) It's hard to understand why HTC just crammed the components into the phone even using glue and ugly wiring. They even used copper foils here and there. Ifixit gave HTC One the lowest ever repairability score of 1/10 which is the 1st from cellphone category. (They said it's impossible to teardown HTC One's back cover without making dents on its aluminum casing. Also, you can't replace display panel without taking out the hard-fixed battery first.) Internal design seems very prone to problems. Below is HTC One's internal amid the teardown process and you can understand what I wrote above.
See how Apple and Samsung dealt with the battery in their iPhone 5 and Galaxy S III respectively. Apple allocated the whole left side for battery while Samsung used the center space for it. PCB board and battery are not stacked as seen in HTC One.
This internal design will cost HTC much in the long run. While it seems very prone to electrical problems with its complicated and crammed internal, it's hard to repair at the same time. That being said, it's easy to predict what will happen if things go wrong in the future. HTC customer service shop may get many visitors as time goes by after the release. But it's hard to replace the components or to repair the broken phones. In the case, the only solution is to prepare large stock of HTC One for exchange.
HTC One's photos below are self-explanatory, so I'll skip writing the comments for them. I don't understand Chinese letters written over photos either. Don't ask me what those mean. :) Anyway, you better be careful when unboxing to avoid the One with defects.