Moral beliefs are only a small part of why someone may act in a trustworthy manner. However, acting in line with one's sense of ethics would be an additional incentive to deal fairly. No, it's not the primary force that makes your bank give your money back to you, that being a combination of reputation, as you say, and the rule of law. All else equal, however, I would expect that someone who believes they should return money they borrow to be more likely to repay a loan than someone who doesn't.