Are Grab/Bolt safer than street taxis?

They are generally more convenient because the price is set in the app, eliminating the 'meter' argument. However, they are often slightly more expensive than a metered street taxi.

What if the driver keeps the meter off?

Tell them to turn it on immediately. If they refuse, end the ride. Do not stay in a cab that refuses to use the meter, as you will likely be overcharged significantly at the end of the trip.

Tipping is not required. However, rounding up to the nearest 10 or 20 THB is a common gesture of kindness if the driver provided good service.

How to get a fair taxi ride in Bangkok

Always insist that the driver turn on the 'meter' immediately upon entering the cab. If they refuse or suggest a flat rate, decline politely and step out of the car to find another taxi.

Use a ride-hailing app to set expectations. Download Grab or Bolt. Even if you don't use them, check the app to see the estimated cost of your ride. This gives you a baseline price so you know if a driver's quote is wildly inflated.
Flag taxis in motion. Avoid taxis parked in long lines near tourist attractions like the Grand Palace or MBK Center. These drivers almost always refuse the meter. Instead, walk 50 meters away and flag down a moving taxi that is already on the road.
The 'Meter' conversation. As soon as you open the door, ask, 'Meter, please?' If they say 'no' or 'flat rate,' close the door and wait for the next one. Do not negotiate. There are thousands of taxis in Bangkok; another will arrive within 2 minutes.
Monitor your route. Open Google Maps during your ride. If the driver takes a strange detour, politely mention you are watching the route. Most drivers will stick to the most efficient path if they see you are paying attention.
Have small change ready. Drivers often claim they have no change for large bills (1,000 THB). Carry 20, 50, and 100 THB notes to avoid being overcharged due to a 'lack of change'.

Are Grab/Bolt safer than street taxis?: They are generally more convenient because the price is set in the app, eliminating the 'meter' argument. However, they are often slightly more expensive than a metered street taxi.
What if the driver keeps the meter off?: Tell them to turn it on immediately. If they refuse, end the ride. Do not stay in a cab that refuses to use the meter, as you will likely be overcharged significantly at the end of the trip.
Should I tip?: Tipping is not required. However, rounding up to the nearest 10 or 20 THB is a common gesture of kindness if the driver provided good service.