It's not a black and and white either you're friend or you're not thing. There are types and degrees of friendship. It's more how much and what kind of friend someone is.
I think, as I understand it, with NTs, it's not so much a wanting to be friends. It's more, seeing a person as a friend, and then taking another step in friendship. Like people may be work-friends, and then they decide to get together for something outside of work.
I think my usual method, well, how they act. If they act like a friend, they are a friend, at whatever level they show friendship. Works reasonably well for the most part. I think sometimes I miss things, but I have enough friends for my tastes. Didn't work so well with one aspie-ish musician I know. Uneven relationship, plus aspie traits, equals too much acceptance of uneven friendship for me to figure out where I stood with him. Until I finally figured out he's okay with unevenness and lack of reciprocity is not rejection, with him.
I guess my expectation of reciprocity is an NT trait, so maybe that's easier for me than it would be for others here, but, still, it's pretty open to conscious observation, seems to me, not something that needs to be done intuitively.
I think maybe the trick is, take little steps to see what the boundaries of the friendship are.
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not aspie, not NT, somewhere in between
Aspie Quiz: 110 Aspie, 103 Neurotypical.
Used to be more autistic than I am now.