A broker's execution model is how your order becomes a filled trade: whether it is passed to external liquidity, matched internally, or filled by the broker taking the other side.
It decides where the conflict of interest sits. A broker that internalises your losing trade profits from it directly; one that routes to a liquidity pool earns from spread and commission regardless of your result. Neither model is inherently dishonest — internalisation is normal for small orders and often gets you a better fill — but you should know which one you are on, because it explains requotes, slippage patterns and why your scalping strategy was restricted.
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Guide
How Execution Models Work: ECN, STP and Market Maker
Market maker, STP and ECN describe where the other side of a trade comes from — and what each model changes about spreads, requotes and order handling.