Never lie on your taxes or to customs.
Brazil immediate turn (PTY-DEN): Customs asked one question: "Did you get your checked luggage?" "Didn't have any." I was sooooo close to buying some Cubans in PTY, and should have. BTW Cuban cigars are only legal if you buy them in Cuba I believe.
Bangkok one-day turn: Customs asked 2/3 questions, took one look and let me by no problem.
China for business for 17 days: Customs asked SEVERAL questions. Where was I, what did I do for a living, etc.
YMMV.