I am doing a MR to GRU with a one nite stay next month.

Just wondering what do you guys tell to customs or passport control (domestic or internationally) when asked about the purpose of trip or "why the really short duration"? Although I have Global Entry but I just got back from Rio (vacation trip; not MR) and got flagged by customs for secondary bag check where they proceeded to ask me about my purpose of the trip, length of the trip etc.

I don't think lying to officers at airport is a good idea but not sure if they will entertain the idea of "mileage run". Especially in Brazil.

How have you guys dealt with this questioning before (if experienced it at all)?