The main protection overall is probably the reversibility of most kinds of transactions in the mainstream banking system (and the liability of banks to customers in many cases of fraud). At least, this kind of policy can be seen as a backstop to particular arrangements and policies like limiting the size or rate of transactions, requiring multiple authorizations for certain transactions, and so on.

The reversibility of transactions has drawbacks (one that's of interest to me is that it serves as one motivation for reducing privacy and increasing data retention).