Talking about nice-ness again

People who are nice are usually good people, the sort of people you want to keep close, but you can’t conflate nice with good. There’s usually an overlap but it’s not the same thing at all. Somebody can be a very nice person yet not be a very good person. And someone can have a severe personality but be most definitely a good person. So do you think you can tell the difference, and how do you tell? Do you use some strategy, are you intentional? Or is it just something you may or may not notice, like a really passive litmus test?