Well think if it is only 850 , pay him ! Frankly my advice is
you should have told him to go to Ida for damage assessment . Even
you go claim insurance, your insurance will not give you as you
didn't go to IDA to file accident report, and repair is done with
proper paper work.
There is alway 2 side of the story also. I got hit by someone from
behind at a junction, which like your case look like some scratches
of the bumper, but what we did was to send my car to IDA for
accident inspection. That when the real damage is full found and
recorded, according to the IDA guy, you can take all the pictures
you want which look like surface damage, but in a full inspection
will review more. Like my case, the bumper is cracked and some
metal damage which is hidden . Well send in to repair to replace
the whole bumper which took 2-3 days. Of course my job need me to
travel everyday to tuas everyday, thus I need car rental. Thus
bumper 1000 + and car rental a few hundreds , he charge to his
insurance.
Well if you want to bang into someone which is your fault, then of
course the other side have the right to claim car rental, because
some people do need a car to move around.