I wouldn’t trust anybody 100%. I think you can trust someone with “this” but not necessarily “that”.
Sometimes you have to take a chance and see how it works out. I’ve got a friend of a friend (and her dog – watch out, record collection) coming to stay with me next week, whom I’ve never met. But I’ve built up a profile of her via conversations and Facebook and she seems to be a very giving person, who is unlikely to rip me off. What’s the worst that could happen? Not much that I can see. There’s an alternative place she can stay if things don’t work out.
Also, I can’t forget, it’s a pretty big deal for her to trust me too.