I´ve noticed that people don´t shake their heads a lot to motion “no.” I have seen some adults do it, but it´s only if their hands are busy typing or writing. Or they are somewhat distracted and not giving you their full attention.
Instead, what is much more common is the finger wag. The index finger pointing upwards , waved side to side to indicate “no.”
My host sister, Lucia, does it all the time.
Have you seen Gin? *finger wag*
Did you want any more ketchup? *finger wag*
Of course, growing up in a culture where the head shake is much more common, I find the finger wag very hard to do. If your mouth is full while eating, and someone asks you if you want any more chicken, you shake your head. Changing that habit would be so hard. Especially since they don´t move their head while wagging their finger. Just the finger wag, no other body motions necessary.