The first are self-evaluations:
do I have time?
what kind/level of friendship is this likely to be?
do I have something to offer this person?
must have the ability to discern opinion from fact
I share those. But I also have a requirement that that they don't treat me badly, or do anything that makes them dangerous or inhibitory to me. But I've been known to distance myself from someone because I got a bad "vibe." I'm weird that way.
I have quite a few acquaintences, fewer friends. It takes quite a lot to get into my inner circle.
But to spend time with me, my only condition is that people do not bore me excessively, abuse me, or piss me off too often. Luckily, I genuinely find most people relatively interesting and usually think of people as 'misguided' or 'on the wrong track' rather than evil or vicious. I try to like people, but the only way to do that is to have a couple of inches of bulletproof glass between them and me.