All you have to do is to trust no one...

There's trusting someone and then putting your trust in someone and then basic trust. Trusting someone is when you can be offered food and not expect it to be poisoned :D. Putting your trust in someone is when you ask your neighbor to stay at your house and watch your wife and kids while going on a business trip. If you don't consider them an acquaintance, don't trust them, if your having doubts don't put your trust in someone. Never trust anyone online. You don't know them, you haven't met them in person. You can apply some basic trust though. For example, if you've been talking to them online for a while and they seem legit, you can tell them a secret you have that you feel won't have any repercussions if they decide to tell it.

Eh I'd argue there are varying degrees of trust based on experience. If you don't know someone then there's limited trust. If you know someone really well then there's a greater trust. Also I think it's important to trust one's self. Have faith in your own abilities that when the shit hits the fan, you've got the juice to get yourself out of whatever comes your way. It makes it easier to give others a little more latitude when you have confidence that they won't be able to interfere with your plans.

I can't say I trust anyone. I try and place my faith in people. But it's not the same thing. Everyone lies. To each other and themselves.

I tend to get a feel for people and for honesty I just trust no one until I get to know them. I've been let down so many times it effected me.