I agree that using a taxi summoned by the doorman at your hotel is usually a good idea. I've always received from the doorman a piece of paper with the taxi number written on it, in case there's a problem. So, when I left the PA in early September, that's just what I did, and it was an interesting trip.
Asked the hotel doorman for a meter taxi to the airport. When I got back to the front door after settling my account, there was the taxi. Hotel doorman confirmed “meter” and gave me a piece of paper on which the taxi number was written. The meter was on when I got into the taxi. As soon as we hit the expressway, however, the driver turned the meter off. I kept my mouth shut, not wanting a confrontation while my luggage and I are prisoners in this guy’s taxi.
We get to the airport, neither of us says anything, I make sure that luggage is unloaded. Then I ask how much. “500 baht.” I reminded him that I had specified meter, and that the hotel doorman had said meter. He said “fixed price, 500 baht.” We went back and forth a couple of times, with no progress. Suddenly I smiled, held up my hands, and said “no problem.” Driver smiled, too. Then I said, “One minute, I’ll get the police.” Started walking towards the terminal.
He tried to block my path and said “OK, how much do you want to pay?” I walked around him and repeated, “No problem, I’ll get the police and be back in one minute.” He started getting frightened, from the look on his face. Repeated, how much do you want to pay? I replied 250 baht. He smiled and said OK.