"All right, here's the loan you requested."
"Thanks, now get out so I don't have to pay you back."
"What? But that's-"
"This is your fault by the way."
This routine was commonplace enough it's even a game mechanic in Crusader Kings.

The last time I checked, Judaism didn't require a mass effort to proselytize anyone. And the whole loan thing was a Christian matter, with Christian lords unable to really place down any profitable loans, but instead forcing the Jewish people that lived on their lands to do them instead.

And when it came time to place the blame on someone for your own faults? Well, there's the Jewish guy who handles your loans that no-one likes because of the fact that he handles loans. It's why there's such a huge influence by Jewish people in Hollywood for example: they weren't given many opportunities for job in other fields, so they took what they could get.