The SM must source 3 quotes. They may do it directly, acting as an authorised representative of various insurance companies, but it is now common for them to offload this tedious task to one or several brokers.
The SM has a duty of disclosure regarding his commissions, but the broker doesn’t. The broker will also charge a fee on top, which is usually disclosed.
It is also important to note that most brokers will only provide “general advice” (as opposed to “personal advice”). In doing so, they somewhat circumvent “the obligation to act in the best interests of the customer.”
In some cases the justification provided for not obtaining 3 quotes is that some of the insurers contacted refused to quote, which may be true, or not.