That's a great question. And it's a really hard one to answer but I look at a few things. First, who really, truly loves your project and wants to see it get made? If a potential co-pro partner doesn't put effort into negotiations and discussions early, they surely won't do much once the...
100%. You always need to go to people you trust and whose taste aligns with yours. Your job isn't to take every note. It's to take every note that resonates and makes the project BETTER, not different. And for notes you are unsure about, wait to see if two or more people have the same note.
You need to constantly stress test ideas early. Start with trusted colleagues; be hyper-open to critique. Iterate and expand outward. If you are starting out, you will likely need to pay for input. That's how you get better. There are a thousand resources here but you need to find people who are...