Final answer:
The substitute decision-maker of last resort is usually the public guardian and trustee or an equivalent public authority, who is legally designated to make decisions for an incapable individual when no other substitute decision-maker is available.
Step-by-step explanation:
When a client is found to be incapable and no substitute decision-maker is available, the substitute decision-maker of last resort often defaults to the public guardian and trustee or a similar government-appointed body. This entity is empowered by law to act in the best interests of the incapable person, making decisions about personal care and managing financial affairs when necessary. It is important to note that such arrangements can vary by jurisdiction and local laws, but generally, a public authority is assigned for this role to provide protection to the individual without capacity.