Better safe than sorry is right, but there are a hats too.
I was a particular flight flying into JFK during school season a lot of Chinese kids. I guess they all like bringing food stuff from home. I don't care for that. I never bring food not even crackers. I can buy all that here in the US why bother. I marked no food and the customs guy didn't believe me. Insisted I was lying and I was going to lose GE. Thanks for being a d bag. Of course searching through my carry on (I don't have checked bags), the guy insisted I was leaving my checked bag behind because he didn't believe that he got a guy who really didn't check any bags and didn't have any food not even water. I wasted I think an hour while the guy insisted something wasn't right until the entire flight had cleared and all the baggage was gone.
Finally the supervisor came in really apologized for the actions of this agent and he got a very stern talking to. What annoyed me most is I had to pay for an extra day of parking. I want my money.