In the DS9 episode "In the Cards", when Jake wants to acquire a baseball card:

JAKE: I'm Human, I don't have any money.

NOG: It's not my fault that your species decided to abandon currency-based economics in favor of some philosophy of self-enhancement.

JAKE: Hey, watch it. There's nothing wrong with our philosophy. We work to better ourselves and the rest of humanity.

Quark is certainly not going to give free drinks to the Humans just because he is impressed with the moneyless philosophy of the humans. I can understand if he gives free drinks to beautiful Jadzia Dax to attract other male paying customers. Other than her, I expect everyone else has to pay. However, how can they pay if they have no money?