How do you know you can trust someone?

Trust everyone to disappoint you and be surprised when they don't

ive been learning not to trust anyone especially people online.. been really burned really badly for trusting people online

Trust is something to be earned

I think trustworthy might be the word you were searching for. Hard to say. Some people have real integrity. Seems a scarce commodity. Be self reliant. You'll be able to weather betrayal and disappointments

experience....trust them with little things and if that works trust them with big things.

You have to make them earn it in small amounts but never in full

Never trust anyone with everything!

Simple: I ask them if they're me.