How do u tell the difference?

When you first meet someone.... How can u tell if they are a N?

I met a really nice sweet guy on the weekend and I didn't get any red flgs or bad gut feelings..... Yet then I've thought about some of the things he said and i start worrying.

Are the genuine honest guys out there who are sweet when u first meet them? I'm confused because the exN was sweet at the start too? How do u tell the difference? I don't want to think every sweet guy is a N?!

Is it just a matter of going super slow??

Advice??