I always use the business professional standards to begin with:
Mr or Ms as appropriate
Reach to shake hands with Mr. wait Ms. to shake hands first.
When my client/customer tells me to call them "jim" that's when I do so and not before.
It's business etiquette and respectful of each individual. Many customers take exception to being "informal" in business. I know I do until I am comfortable with the person with whom I am doing business.
And I do business in a beach/tourist community where everyone wears shorts and t-shirts and sandals. Except me of course
Good topic.