How can you tell on an oncoming vehicle if they have their brights or high beams on and don't just have really bright headlights, as most trucks and SUV's have now days?
Put your own main beam on ( tin hat on ) - if theirs then get brighter you will know they had theirs on dip.
Seriously - dont go dazzling other road users - the only time I would intentionally dazzle another road user is if I were being dazzled by oncoming traffic and was in danger of losing control - It would probaly let them know their main beam is on or their headlamps need tilted down due to the weight/no. of passengers being carried if they have forgotten to do so.
Sometimes drivers inexperienced with night driving forget. I try blinking the high beam on very briefly before a critical distance and this usually prompts an informative responce. If need be I slow down to a speed where I can respond to anything that may become a safety issue. I'm perfectly willing to let the next person behind me deal with any road rage issues.
If an oncoming vehicle is dazzling you you have a dangerous situation because one of the drivers has restricted vision, if you then retaliate by dazzling them you then have a VERY dangerous situation two drivers with restricted vision.
A very quick flash of your main beam should do the trick.