How do brokers earn money?

Brokers earn via bid/ask spreads (0.5-2 pips per trade), commissions ($3-10/lot), overnight swaps, and inactivity fees. Market makers profit from client losses or hedging spreads. STP/ECN pass trades to banks for markup. Zero-commission hides wider spreads. Volume drives revenue—active traders pay more. Regulated ones disclose all fees transparently.