I travel to Thailand every year, and have family there. The only problem I have ever had with a taxi driver anywhere in Bangkok is a refusal to take me because the journey was too short - even that has been fixed at the local shopping mall with a cab rank where it is mandatory to take any fare.
When meters became compulsory a few years ago, the overall cost of journeys actually dropped. The majority of taxis are leased by the drivers (the green & yellow ones used to be owner operated, but now I'm not so sure) on a daily basis. It's a real grind to make a baht ....