It is the luck of the draw now, as they scan all bags, which wasnt the case a year or so ago.
If you have a foreign passport that also helps, as i brought back a sewing machine for a friend from colombia, and had a whole of electronic crap in my bags, which the customs guy was interested in, but all he did was ask where i was from, and then said i could go.
No so lucky for alot of people infront of me, especially the ones with LCD TV in hugh boxes..