Their suspicion might come from t.v. shows or other reports they hear of narcotics be smuggled through the freight industry. The other day I saw around three state trooper's who stopped a truck and proceeded to hit the tires with their baton's to see if their were drugs stuffed in the inside of...
I agree with the advice stated above. Also, being that this would be your first offense, you'll have a better chance in court. Your "buddy" deserves to be prosecuted for the crime HE committed. I believe the jury will sympathize with your side because you have no priors. Good Luck!