This is similar to a question I get all the time, which is how to pick critique partners and how many I use, including beta readers, etc.
The short answer is that this has changed quite a bit over the course of my career. I've been a member of two different critique groups that met IRL, and I've been part of various clusters of critique partners and beta readers online.
Another short answer is that who I discuss my ideas with or share work with at various stages changes all the time, and varies depending on the type of story and what I need help with. I'm blessed with a number of writer friends at this point who can read for me, and give me what I need, usually blazingly fast, too.
I can also say that I've grown extraordinarily picky about who I bounce ideas with and who I ask to look at early drafts. This is because - and I've used this analogy before - stories in their earliest stages are like infants. Their skulls are still soft and they are fragile beings that must be carefully tended. Just as you'd never hand your newborn child to just any person on the street, you don't want just anyone giving your fragile new idea a good, hard shake.
There is a time and necessary function to the good, hard shake - but that's akin to the college years, when you figure they've got to get drunk and pass out on the couch at the fraternity house at least once and learn some lessons from it.
But not the baby story. The baby story needs love and nurturing. It needs someone who can see the potential and not that dreadfully bulging forehead. I even left one IRL critique group because I felt they were having a negative impact on my work, instead of a positive one.
That's not the topic question, though, right? The question is how do you know who to trust?
There are no easy or short answers to that one, though I'm very much looking forward to hearing what advice my fellow SFFers have to offer. It took me a long time to decide to leave the crit group that wasn't working for me. It can be difficult to separate the very real reaction most humans have to criticism from the intuition that something is having a very real negative impact.
None of us like to have our work criticized, even if we are privately pissed that they passed out on the fraternity house couch. Learning to receive criticism and use it effectively is a huge part of learning to be a professional author.
But not all criticism is useful, and it's not always kindly meant.
So, that's how I decide: I consider the source and their intentions. If feedback from someone feels negative or unkindly meant, I pay attention to where they are with their own work. Are they feeling good about the work they're doing? How do they critique other people's work? Are they otherwise supportive of me and seem genuinely pleased for my successes?
That last question is key, and helped me to decide to leave that group. When I mentioned a success, these same people were sour and unsupportive. I knew then that their criticism of my writing felt negative because it was.
When you figure that out, walk away. Don't trust them with anything fragile again.
