The modern problem is in large part, scale. Trust works better in smaller communities and at smaller scales - people are more likely to be willing to fleece someone they don't know and will never see than their family, neighbors, or the person standing behind them in line. When there are immediate and permanent social consequences for violating trust, it's much less likely. The community (or tribe, if you prefer) scale is the scale that comes naturally to us.

A lot of 'social technology' exists, in part, to help increase our ability to scale trust up. This includes things such as nations and religions. As people become more irreligious and nationalism declines (including into an us vs them mentality within the nation - simple cheerleading of your country is not what I mean by nationalism), trust declines, and people are more likely to scam, grift, and fleece others. And once it is gone, it is very hard to get back.