From vanilla to discussing kink

Hey! I'm new to this, and I'm a little curious how people normally go from the vanilla intro into discussing limits/ideal partners?

My current methods at finding a like minded kinkster involves subreddits and other apps tailored for that exact purpose. To me, the pretext implies discussing boundaries and limits is hugely important, but from the 4 or 5 conversations I've had it is usually deferred to "when we get to know each other" (which is understandable, as everyone should feel comfortable). It's just a little confusing to me, so any insight is much appreciated!

What are some big green flags that the person is worth your time, specifically from the vanilla side of conversation? Also, what are some of your favorite vanilla intro subjects or conversations you've had?