Your co-workers aren't customers

"Sales has asked that we stop sending bills to their accounts."

"Wait.  What?  Why?"

"Well, according to the sales guys, when the customer feels like they owe us something, it's harder to make more sales."

"Sales that the customer doesn't want to be billed for?"

"Exactly."

"But how are we supposed to get the customers to pay us?"

"Look, the sales department is our customer.  And we have to meet their needs.  So let's make this happen.!"