if this is in the US, wouldn't this expose the airline to charges of false arrest?

In stores there is something called "shopkeeper's privilige" that lets the store reasonably search you if they believe you have stolen something, and detain you for the police. But I don't think they have this on airplanes.

I certainly wouldn't like it, and I wouldn't want anyone searching my stuff either unless they had a warrant. Ha ha ha ha -- that was a funny joke!!!