Something I've been pondering.

When I was at a session, being trained in customer service, the person teaching said something that made me think. He noted that every time you give your eftpos card or something to the seller, they give it back, and you say thankyou. He noted that you've just given them YOUR money, and YOU are the one that said thankyou. That made me think, who should be the one saying thankyou? Should it be the seller, who has just received the other person's money, or should it be the customer, who has just received the other person's product. He thought it's pretty funny that the customer would thanks someone for taking their money. I think both should be saying thankyou, both have done a service for the other. What does Southperry think?