While we could say it's more 'worrying' that there are quite a few teenagers getting customs, it would rather simplistic to focus solely on the fact that perhaps only they shouldn't be getting this type of IEMs. There are people in their 20s & 30s (and older) who are also purchasing customs. I insist - it's true and a valid argument that it's ultimately their money and they're free to do whatever they see fit with it. But to say it's 100% their mistake if they're not happy with the end product, for not properly doing their research, isn't entirely true/fair.
Even these adults can be (easily) misled. Researching into the subject of customs isn't as easy as it seems. A lot of - if not most - online reviews unanimously praise customs. In many cases these reviewers got free samples (in exchange for free marketing). It's not always easy to find true unbiased reviews. I'm not necessarily suggesting that unbiased reviews would ultimately agree with my own particular views on the subject, but those reviewers are often given special treatment by the manufacturers. Manufacturers try and make sure those review samples are in perfect condition both cosmetically & in perfect working condition, ie excellent QC for that particular review set. These reviewers will also get their customs quickly and any possible issues with refits will be sorted out in a timely fashion. These great reviews will also likely guarantee than any future models are given away to the same reviewer/publication, which in turn means more marketing for the manufacturer in question.
Then there's the subject of shilling, which we have seen on HF on several occasions, it is sometimes pretty easy to spot but quite a few times, unfortunately, it isn't. True, shilling is not exclusive to the world of customs, but unlike so many other consumer goods, where, for instance, you can get plenty of reviews on Amazon or elsewhere by real consumers, it's very unlikely we will ever see customs reviews on Amazon. Yes, I know there's also shilling on Amazon and elsewhere, but when a product is quite popular, chances are we, the consumer, can more easily 'separate the wheat from the chaff'.
In addition, some of the people who have had less than stellar experiences with their customs are not always willing to express their real views and come forward, perhaps out of sheer frustration or the feeling of being unable to articulate and convey their disappointment, or possibly feeling intimidated by those who seem to know more than they do - some will simply try and sell their used sets (at a huge loss) and possibly just try and forget about their bad experience and stay away.
It's also not uncommon that when a poster expresses their negative views they'll be met with a bunch of replies by some of the fanboys of a particular custom IEM, or they'll be told they have a wrong fit, wrong ear impressions, or that maybe the sound signature is not for them, or to give themselves more time to adjust to their customs' sound signature & fit, or that they need to change sources, get an amp, use lossless files and so on. These fanboys at times behave like 'gangs' and they'll make a point that the unsatisfied HFer is just an isolated case.
Some of the people who genuinely hear a significant difference in SQ from their top-tier universals to their customs - ie, people not easily influenced by hype - often had a poor/wrong fit with their universals as was suggested by some people in a couple of posts at the beginning of this thread. There are cases, too, of people had a good fit with their top-tier universals (my case) but some of those universals just weren't good enough and therefore they do hear a significant difference in SQ. That was my case with the SM3, SE535 & SE530, where my custom ES3X sounded much better. But, unlike the case with customs, where if you don't like the sound signature, selling them will represent a huge loss. I sold all those universals I didn't like quite quickly and didn't lose that much in the process.
In my particular case the UM3X, TF10 & CK100 delivered between 80-90% of my ES3X's SQ, the W4 about 95%, and the EX1000 deliver 100%. The W4 & CK100, BTW, do not come with detachable cables.