I am reading a book that gives the same advice~

The book is called

The first trick listed in the book is:

"The old-fashioned instant grin carries no weight with today’s sophisticated crowd. Look at world leaders, negotiators, and corporate giants. Not a smiling sycophant among them. Key players in all walks of life enrich their smile so, when it does erupt, it has
more potency and the world smiles with them."

Technique #1

The Flooding Smile

Don’t flash an immediate smile when you greet
someone, as though anyone who walked into your line
of sight would be the beneficiary. Instead, look at the
other person’s face for a second. Pause. Soak in their
persona. Then let a big, warm, responsive smile flood
over your face and overflow into your eyes. It will
engulf the recipient like a warm wave. The split-second
delay convinces people your flooding smile is genuine
and only for them.

haha