Yep. After a person posts that they've been playing for x years and still cannot get a good tone or control their intonation, it's a good idea to reconsider whether "self-taught" remains a prudent path to practice. They don't have to take the advice, but maybe it's worth a thought to get them on track.
For those that take pride in flailing their way through mediocrity, go for it. I would get frustrated and quit (like I did with my first guitar that was really quite terrible). I support their endeavor as long as I don't have to listen to them.
Well, this is kind of where I was when I graduated college; I'd been playing a TON of gigs for six years, and people generally liked what I was doing, but I wasn't satisfied with my tone (intonation was never a problem).
When I took up seriously playing baritone, it became apparent that I needed to get a grip on the fundamentals of this thing. I decided (whether rightly or wrongly) that having read all the appropriate instructional literature, I didn't necessarily need to take formal lessons to get my embouchure and airstream worked out; but that what I needed to do was to PRACTICE, seriously, with ATTENTION and INTENTION, to take those lessons I'd read about, and understood intellectually, and INTERNALIZE them to my own personal structure.
So, that's what I did, in those hours in the practice room, or out on the city park soccer fields doing interval studies and long tones.
Was that "self-taught"? I mean, you could say it was, in the sense that I did not have a formal lesson every week with a teacher telling me how to form an embouchure, how to breathe, how to get my finger action efficient. But on the other hand, you could say I was taking lessons from Larry Teal, Sigurd Rascher, Lennie Niehaus, and a number of other famous saxophonists, just second-hand by reading their words. In the end, the only way I was going to internalize how it feels to play with a good embouchure, good airstream, and adjust voicing to hit intervals without bobbles or squeaks, was to spend that time by myself in the shed, whether with or without weekly lessons. So in that sense, we're all either "self-taught" because we've spent that time in the shed (whether with or without weekly interactions with an instructor), or we're "self-untaught" because we haven't spent that time in the shed (whether with or without weekly interactions with an instructor)>
After all, you can take weekly lessons with an instructor for years, but if you never go off by yourself with your instrument and practice the exercises, you won't magically be able to control tone, or intonation, or have clean technique. You'll remain "self-untaught" no matter how much you spend on lessons, if you don't PRACTICE.