I'll give you a scenario that could happen and ruin someone's career:
Let's say I work at a summer camp with an athletics program. I am a college student in my early 20s, and need the job to afford everything. I play competitive college golf at the same university that hosts the camp, which requires the players to be amateurs under the rules. I am given the task of leading group lessons for kids aged 5-8, since none of the other counselors know shit about golf and I'm really good. One of the other schools finds out, knowing that I'm a threat to their team, and reports this so that I get declared ineligible, or at least provide a big, stressful distraction that could ruin my career. I can no longer play college golf, so I have to pay a lot of money for a range to practice that a college student doesn't have. I lose my university discount, and can't even play amateur tournaments to practice anymore. I need to join a mini tour just to continue to develop, which costs as much, if not more than my tuition. And of course, I need to either finish school or go straight to pro playing, either of which will put me in tremendous debt. Not to mention I lost my team and coach, possibly scholarships, and went through this whole ordeal, which would rather sour me towards the sport. Even if I regained my status, I could miss tournaments as a result.
Now, before you all check the rulebook to try and prove me wrong, I'll admit; there's a rule in the books specifically about summer camps.
That said, what's to stop a parent from asking for private lessons because little Matt likes you and really seems interested in the game? You need the money being a college student, I'd be willing to bet the private lesson one hour a week would pay more than the day at the summer camp, and give you 7 hours to practice. What about Matt's brother, trying to make the high school team? How about his dad, who really wants to learn to play better so he can share in his kids' interests? What about your own brother? Surely none of those are bad choices, they'd all help grow the game and have a positive effect on the others. You'd be a mentor, share your competitive experience with a kid who's where you were in high school, and help a dad connect with his kids and learn a game that keeps him healthy and entertained for years.
Just because you're getting paid for lessons doesn't mean you actually know jack about the golf swing, even knowing how to play well enough to pass the PAT doesn't make you qualified. You could give those lessons, as I understand the rules, as long as you took no money for them. How the hell could you do that? As a college student you don't have the time to do stuff like that. I'm not sure if you could accept equipment or a membership or something as compensation. Yet there are rules essentially allowing one to negotiate a sponsorship as an amateur that goes into effect once you go pro. It seems like they're so strict about actual amateurs, but if the player is going to become pro, they don't care. As long as it's done under the table, it's fine.
And the most annoying part of all this is that gambling is never taken seriously, even though in some cases one can make more money from it than actually being a professional. It's common, yet completely ignored.