Some years ago NewMexiKen made several overseas trips with a diplomatic passport. In all my comings and goings I had my bags searched only one time. Arriving from Europe at Dulles International, I wasn’t sure whether one of my bags was on the plane or had come ahead. Further, someone was picking me up and I knew they’d be cruising the airport, around and around. By the time I’d finally located my bags, I was visibly anxious. Sure enough, my luggage was searched by a very determined customs agent. (I was, of course, totally innocent of any wrongdoing.)
The article linked-to above says the TSA employees get only four days training and three days of field practice before being assigned to face watching duty. That doesn’t seem like anywhere near enough, but I do believe experienced personnel can become very good at spotting the nervous and otherwise pre-occupied traveler.
I also believe an experienced perp can learn to be dispassionate about anything.
There was one program that was going to run everyone through a few questions real quick, to boost reactions for study.
“Have you ever lied to authorities?” “Of course I have!”
…
Analyze that.