While the concerns here are appreciated, if the provider doesn't know you well enough, it is her prerogative to minimize her risk. Unfortunately, there are lots of people who refuse to take proper precautions, for whatever rationale they choose. It becomes her choice to limit her exposure, and the client's choice to accept the terms of service. Or not.
It would be interesting to know if those who visited spas without a mask requirement had developed a consistent business relationship, or if the encounter was random.