Liability for the professional that knows if they botch a job in horrendous fashion that they could lose the ability to continue practicing their profession.
But it's not certain you would even be able to continue to do the job if you botched things in a horrendous fashion. There is precedent for individuals being barred from working in certain industries if it is considered necessary to protect the public, even when those industries are unlicensed. Granted, it is rare and a lot more complicated than where licenses are found, but if you've botched things in a horrendous fashion anything is possible.