It can be much more than just $1....

The so called "fast meter" is mainly related to older model taxis as the DLT was considering to introduce a night rate about 16 years ago, so many of the taxis from this period have meters which are pre-programmed for a dual rate. (I'm leaving aside meters which have been intentionally rigged - a very serious offence in the eyes of the police). These older meters start button has to be pressed 2 or 3 times (depending on the meter model) to have this rate activated. Some have had new meters installed since so will not have the dual rate.

Basically, there are 3 models of registered taxis in BKK between the 20+ taxi companies and the owner drivers (yellow & green taxis). Newer models taxis from 2017/8, medium aged models from 2008-10 and old taxis from the turn of the century - early 2000s. It is these older taxis which can have the pre-programmed dual rate.
(You'll even see a few even older taxis from the 90s but they all tend to be unofficial, i.e.. unauthorised ones.)

There are a few simple steps which you can take to avoid this problem - which is as widespread as before in my view;

1) Only use new taxis - which are generally a more comfortable ride with better aircon,
2) If you do use an older taxi and the driver presses the button more than once to turn on the meter then that is a warning sign,
3) Use the 555 guide (prior to the last fare rise - which wasn't a rise at all but reduced the 35 baht initial fare distance from 2km to 1km - at 5 kms the fare was 55 baht. Currently, at 5 km the fare should be 57 baht! (This is excluding prolonged stoppages and the time charge per min). If the meter is between 57 and say 65 baht then you are okay. However, if it's 75-80 or higher then you are mostly likely being ripped off. It's not much of a difference if you're only going 5-8kms, but if you are doing 12-20km+ it will be an relatively significant difference. Two or 3 times the fare depending on the distance. 50% of taxis do carry the DLT distance fare table....probably another potential warning sign if your taxi doesn't.

In summary, new taxi, meter activated with one press and 555 guide.

Most drivers have given up on this tactic as they find plenty of gullible pax who stupidly agree to a fixed fare (unlawful pursuant to DLT regulations). Why run the risk when plenty of pax agree to 500 baht fare to and from the airports for fares which would be 200-250 baht on the meter. There's a reason why at any given time there are around 3k to 5k taxis waiting for hours in the taxi car park 2km from BKK terminal.....