I recently returned from the US with two bulging suitcases full of internet purchases. My trip was almost ruined at the Barcelona airport when I accidentally managed to catch the eye of the customs inspector while walking through the "nothing to declare" lane.
"Where are you from?"
"Err... the United States?"
"Hmmm." He examines the tag on my suitcases. It says "FRA/BCN" (I had flown via Frankfurt)
"FRA" he reads. "Is this from France?"
"Err, no, Frankfurt"
"Ok, go ahead"