When returning from an overseas contract with more suitcases than I went out with: I had kept all the receipts, put them in a spreadsheet and handed the whole thing to the folks in the Red Channel. They were lenient on the list and did not search the bags - in which I was not hiding anything. I paid by a credit card that scored airmiles. Honesty worked.
In the late 80s, returning from a long weekend in Geneva with my then girl friend, we went through the Green with no suitcases. We were stopped and, on looking at my passport saw that it was my birthday. "What did you buy in Geneva?" We replied nothing as it was too expensive. They asked to look at my wristwatch and saw it was old - about 17 years at the time. Seeing the old watch, "What watch did you get for your birthday?" I said, None, this works fine and Geneva was the birthday present.They started to search our bags watching us carefully.
They were sad that we had nothing to hide. Perhaps others had slid through whilst they searched us!