Take picture on the spot with your phone and measure the height of the door corner to the dent of your door. He can't deny.
There was a time I was sleeping in the back seat of my dad's car while my parents went into T&T, then I heard and felt something hit the car. I woke up and saw it's the door of the car next to us. After I got out of the car and talked to this mainlander, he offered to give me $5 to the chipped paint on the door handle. But $5 is not enough to buy the paint pen from the dealer and his attitude wasn't apologetic at all, so I took his driver license and insurance and report to ICBC to repair it just to teach him to be careful and understand his wrongdoing.
The final cost was like $300 something and the trouble for us to get it repaired. If he was apologetic and offered to pay $20 then we both don't have to suffer.
You just have to be prepared to call police is he runs away. Always take a picture of the license plate before the talk, and it's a good idea to have at least one auto upload photo service (dropbox, google+, or facebook) on your phone so that if he grabs your phone and destroy, you can still have record.
You don't always have to call the police, but there are key situations in which you're required to make a police report like when:
there has been a death or someone has been taken to the hospital by ambulance
it was a hit-and-run accident
someone broke into or vandalized your vehicle, or
your vehicle was stolen.
In addition, a good rule of thumb is to call the police if you think the damage to your vehicle looks like it may be more than $1,000 (or $600 for a motorcycle and $100 for a bicycle).
(<<< My last car at last determined total loss but no police showed up on accident date)
If the police don’t come to the accident scene, your Dial-A-Claim adjuster will let you know if you have to get a police report.