What are the concert rarities I should look for? I'd hate to walk past something not knowing what it was
Then read up. Do a bit of research. Like the rest of us had to do before the internet existed so that we'd be here to spoonfeed you now.
I know this makes me seem like even more of a git, but you'll retain the information better if you've had to find it out for yourself, plus you might find out something tangential that you find interesting as well.