I used to cross the border almost every weekend and rarely got searched. One time, on the way back to Canada, the Customs agent I was talking to had a sense of humour. She said "Ding ding ding, you are a winner today!". I said "What do I win". She said "A free inpsection". She then went on to explain that on that particular day, every 100th vehicle to pass through had to submit to a thorough search.