Commission – A transaction fee charged by some brokers on each trade, usually a fixed amount per lot or a percentage of trade volume. For example, a broker might charge $7 per 1.0 lot round-turn trade. Commission-based pricing is common with ECN/STP brokers who offer very low raw spreads; instead of marking up the spread, they charge a commission. In an ECN account, spreads are tighter but you pay a separate commission. When evaluating a robot’s performance, you should account for commissions in addition to spreads, as they increase the total trading cost (especially for high-frequency strategies).