Speaking anecdotally, I became significantly more prejudiced against Jews being "all like that" when I became friends with about half a dozen Jews in college. After I had been ripped off for about the fourth time, it became very apparent that social attitudes towards what was "fair" and reciprocatory behavior was taught differently in Jewish society - and I adjusted my behavior accordingly. Less eloquently, I assumed every deal they offered was a shitty one for me, and never expect reciprocation in the future for anything. Prejudice against Jews has thusly served me well in my adult life, as I have had business dealings with Jews several times and suffice to say contractual negotiations are significantly lengthened and much black marker is applied.

As I studied game theory later picking up an economics degree as my 2nd major, I would later learn that ideas of a "fair deal" are indeed societal constructs with very large variations across different societies in the world, and indeed studies show that Jewish societal conventions when it comes to money and fairness is an outlier across a large variety of situations. It's not that Jews don't have a notion of fairness, it's simply that their notion differs wildly from the cultural norms of almost everyone else.