I have had a few clients attempt to refuse to get clearance for known conditions. I will not work with them without the clearance. I apologize to them for not being able to work with them without. I say, “I am so sorry. But without the clearance, my hands are tied. If you change your mind and go to your doctor, let me know.” And I leave it at that. I can only think of a few people who never came back with clearance.
Personally, there is nothing a client can pay me to not handle their health as safely and professionally as possible.