Reddit hates being sold to. Founders still find customers there every day. Both things are true. The difference isn't luck or a secret sub, it's method.
What "that guy" does
You already know the patterns, because they annoy you too:
Mods remove all of these on sight, and even when they don't, readers do the removing with downvotes.
Help first, mention second
The method that works is simple to say and harder to keep up: be useful far more often than you promote. If most of your comments help people with no agenda, the occasional time you mention what you built reads as a recommendation, not an ad. Trust is the currency, and you earn it before you spend it.
Earn the right to mention your product. Don't take it on the first comment.
How to mention it so it lands
The real work is finding the right thread
Most "self-promotion" advice stops at how to write the comment. But the comment only works if it lands on a thread where your product actually fits, while that thread is still alive. Finding those, across the handful of subs where your buyers hang out, is the slow part, and it's where most people give up or start spamming out of impatience.
Karmy does that part for you: it watches the right subreddits, surfaces the threads where you can genuinely help, and hands you a draft that leads with value. You stay the helpful one, not "that guy".