When you are unable to see within a vehicle due to a combination of darkness and window tint, order the driver to turn the interior light on and lower the windows. If the window and/or interior light does not work, order everyone’s hands on the windows. Having them open all the doors is not the best or safest thing to do, but I’ve seen it happen.
You can also wait for backup.
Make sure that your flashlight is one that’s powerful enough for you to see in the vehicle and temporarily blind someone inside.
There is an issue with extended cab pickups, since most have extremely dark tinted rear windows and it is very difficult to see anyone in the rear seat. Ordering a driver out of the vehicle in that situation can make things a little safer. Practice this on a friend’s vehicle.