Anyone who has dealt with this thought to write to Michael Bayley? It's easy enough for them to have a statement in the Compass about declaration and how to go about it prior to debarking. If they get enough complaints...
One trip, back when we were still doing the forms, we had bought over our limit (by a couple hundred dollars at most I think and we were honest) in port, not onboard, and when we turned the form into CBP, they pulled us into an office and wanted us to pay in cash something like $12.75. They had no way to give change so we ended up giving them $15 or something. They didn't like that, but they couldn't have been surprised. We do carry cash, but not coins. We usually stay below the allowance and never buy enough onboard to trigger anything. We also avoid buying much in the duty free shops in port.