As a side note, coaching/instructing, I prefer to see myself not as someone who points out errors, but solutions!
As to finding oneself a mentor instead of a paid instructor, needless to say, if one gets lucky, it may be the best that can happen to an aspiring player.
Unfortunately, when I was a teenager taking up pool, I couldn't find a single person who'd share any secrets, even less so when it turned out I was beating everyone in the neighborhood within a year. At that point, boarding a plane to get some serious instruction abroad seemed (and turned out to be) the only choice. In hindsight, I was probably lucky none of the locals was willing to share their knowledge with me (such as that "one must jab at the ball and pull back the cue as quickly as possible to get draw on the cue ball" or "always aim at the center of the cue ball regardless of what spin one is applying, in order to baffle one's opponent"?!). Today, after more than a quarter of a century, some of those people still come to me to take lessons. And it's not because I beat them as a teenager, nor because I might still be able to beat them today.
Greetings from Switzerland, David.
_________________
„J'ai gâché vingt ans de mes plus belles années au billard. Si c'était à refaire, je recommencerais.“ – Roger Conti