pois não

From pois (“so, then”) + não (“not”). Probably originally intended as: "so ... not ...?", implying either "so, how could I not serve you?" or "so, how could I not do what you asked?", depending on the context.

Compare Spanish ¿cómo no? (“how not?”) and Hungarian hogyne (“sure, of course”, literally “how not”).

pois não?

1. (Brazil, formal) Can I help you? (used when attending customers)

pois não

1. (Brazil, formal) yes; of course (used to confirm a request)

   “Eu gostaria de uma salada.” — “Pois não, senhor.”

   “I would like a salad.” — “Yes, sir.”

Don't confuse with pois sim (“used as a sarcastic agreement of something that is obviously to be disagreed: yeah, right!, yeah, sure!”).