My point is that there are very few cars manufactured today that do not have a speedometer error of +/- 10km/h. There are allowances for this in the fact that officers only ticket people going over a certain speed above the limit. The analogous allowance by customs is by providing a multitude of big signs, plenty of opportunity to dispose of contraband even up till the moment of inspection.

OT: On the QF flight, the Snack on Q bags are handed out after dinner when everyone is sleeping (I know because I was in a deep sleep until the FA threw one at me in the middle of the night)? And the arrival cards around breakfast time? At least that's the way I remember it with my last QF LAX-AKL flight in late 2006.