When at the end of the transaction the customer says, “Thank you,” “No problem” is not an appropriate response.
Of course it was no problem.
“No problem” implies you did the customer a favor.
You’re not being thanked for doing the customer a favor.
The customer is thanking you for the service you just provided them.
Your words probably are the last the customer will hear before leaving the store. As such, they play a significant role in defining their shopping experience.
I’m just sayin’….