>doing medical treatment of oneself's body without any kind of possible insurance
Only if you want to be sold for organs after putting into sleep with nitro gas, because nothing stops underground clinics from doing so, especially if you're no one to them.
Like any other illegal enterprise, they would rely on reputation and word of mouth, possibly even only admitting patients with a reference from another longterm patient. That's how they'd build a clientelle and make money. Why would you let someone with no licence AND no reputation cut you up in the first place?
I think they're broken.