for our own sake - take the second, third or fourth cab

Agreed under "normal" conditions (on the street, waving down a moving cab), but in those places where there are "managed" queues, like the airport(s) which this thread is generally about, then one often has very little wiggle room.

That said, anywhere there is a managed queue (shopping mall, transpo. terminus, etc.) I still state my destination and desire to use the meter, along with any routing options which might involve addition cost on my part. If I sense any trepidation I move down to the next taxi in the queue.

At the airport I have, and will continue, to refuse to accept the "larger vehicles", so I just head back to the queue. My last two arrivals I've had larger vehicles forced on me (single person, one rollaboard); the first time the driver demanded 700 THB once we were rolling. The second time, once I saw the Toyota Innova waiting, I simply and politely declined and returned to the queue.