Shirley, you jest.
Doctors are asked to perform "demo surgeries," all the time.
Lawyers are asked to argue "demo cases" in court all the time.
Social workers are expected to help patients through trauma, in "demo therapy sessions," all the time.
CEOs are asked to do "demo IPOs," all the time.
CPAs are asked to do "demo audits," all the time.
In case no one realizes, that was all a joke. Of course, none of these happen, IRL.
I can see people with no track record (like just coming out of school), needing to do this kind of thing, but, once we have some accomplishments under our belts, we can have some track record.
Some of us may even have significant portfolios. Mine is so complete, that you can easily tell what I can (and can't) do, without ever even contacting me.
Designers live and die by their portfolios. Any first-time designer is expected to have a portfolio to show the prospective employer. Once the designer has been working for a while, they can point to their track record.