I keep hearing shelter dogs are different, obviously trauma changes things. What are things to look for?
Spend time with the dog. That's the key to success, ask if you can take it for a walk (with a volunteer ofc) etc. You'll find out a lot about the dog!

not 100% reliable. people also really need to compare any available individuals with "the breed" they think they like, because they will vary so much.
Of course. Also, if you're gonna get one from a breeder, might as well check out the parents (at least the mum).