"Pois Não" , an expression with two meanings:

This expression is also used in a store for example,when the salesperson greets the customer with " Pois Não?" with a question intonation, this phrase "pois não" is equivalent to "How can I help you?". Without the question intonation ( i.e., as an affirmative ) ; "pois não" is used as a positive response to a request, as in the example below :

A : Você pode me passar o sal , por favor ?
Can you pass me the salt , please?

B: ( giving A the salt ) Pois não.
Of course. Here it is.

Ref: Beginner's Brazilian Portuguese