I nearly had that happen with a rental car. I was living in California at the time but was back in Buffalo visiting my parents. I went to the drug store to pick up a few bottles of Acetaminophen with Codeine as my then wife had torn her rotator cuff and it was before surgery. Like a dolt, I claimed all 3 bottles. I was immediately instructed to pull in a garage, and dogs and mirrors came out and the border agents when through the car bumper to bumper. End result, I had to pour two bottles in the toilet and away I went with the one bottle. Of course, a couple of days later we went to another crossing near the 1000 Islands, didn't say a thing, and had 3 extra bottles.