How do prop firms make money? A deep dive into the business model

Summary: it turns out to be quite profitable for prop firms to charge prospective prop traders non-refundable "evaluation fees" to try and join the firm - which only a single digit percentage of traders will pass.

Even if a trader passes the test, the firms can have charges and ongoing subscriptions and also may do dirty tricks to avoid paying out the prop trader's commissions (of the trading profits).