My mum likes to be called ‘Mrs Lee’ when she’s dealing with anyone in a businesslike way – she was Mrs Lee throughout her working life, and now in retirement, as far the people who paint her house or fix her car are concerned, she’s Mrs Lee to them, too.
Even though first name terms are much more common in today’s business circles, the spirit behind this distinction is useful: business and personal relationships are different, and it doesn’t serve you to mix them too closely.