Trust is a fascinating topic mingling, as it does, personality tendencies (especially extent of projection of one's own evil impulses and thoughts) with cultural or subcultural norms and rational expectations. There are trust cultures and distrust cultures.
Here's a study by nationality: Do You Think Most People Try to Take Advantage of You?
Life has slowly taught me to be less trusting than I am naturally inclined to be, given my cocooned upbringing. I am most trusting, rightly or wrongly, of my own sort of people amongst whom, on the whole, there are strict and agreed-upon codes of behavior.