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I've been in secondary a number of times (business related, frequent border crossings).

They're not interested in you as a person, nor are they interested in holding anyone. They're entirely interested in detecting fraud and crime, and the people are secondary to that.

When you're in there, keep that in mind. They don't care about you as an individual, in a completely neutral sense. Just take in the surroundings (ever notice that it's just a normal workplace to them? Seems weird, but they're mostly relaxed at the office), and answer questions comfortably and respectfully. You'll be out in good time, depending on the lineup.