Focus areas: Payment processing, regulatory compliance, data integrity, API design.
What they value: Correctness over speed, idempotency, audit trails, security.
Common topics: Design a payment system, design a ledger, design fraud detection, design a money transfer system.
Tips: Focus on reliability patterns. "Idempotency keys prevent double-charging." "Dual-entry ledger for audit." "Encryption for PCI compliance." Fintech penalizes "move fast and break things" thinking.