Referrals are the best leads and the least predictable. They arrive when a client moves or a partner remembers you, which is not a plan. Your own marketing gives you control and a second job: ads, a landing page, phone verification, duplicate checking, follow up. Brokers who do this well are running a small agency alongside a brokerage; what the search side involves is under Google Ads for mortgage brokers. The free end of it is covered under how to get free mortgage leads.
A campaign run for you replaces the second job with a price per lead. You define the lead, agree the price, connect your CRM and call. What you give up is control of the ads. What you keep is the only part that was ever yours, the conversation. The model is explained under pay per lead in Australia.