If its not your fault, especially when its parked and you are not even in it, then your rates won't go up.
it also depends on how much the repair costs.
my wife backed into a car in a minute mart parking lot, we are talking a love tap, I wasn't there, but it was a small dent in the trunk.
apparently the guy came outside freaking out saying it was a MINT condition (of course) 1 owner car. (It was a 92 oldsmobile cutlass ciera by the way).
he insisted that she stay there until the police arrived (which was not necessary). He even made the cop take pictures of it, (my wife said the cop was chuckling about how this guy was so concerned).
anyway a few weeks later I checked with my insurance agent, she said it was a $1480 repair
(had to be about the value of the car).
I am sure he took it to the most expensive places. He was "so concerned" but I bet he has not repaired it and just pocketed the cash.
SO, what I was told by my agent, is that if it is under $700, no increase. over $700 and it will increase. my wife lost her "safe driver discount" which was $16 a month.
THE trouble with dealing with "nice people" is that they can turn into real jerks in a hurry. at first it seems like they want to help, then they don't return calls etc etc.
as long as you get it in WRITING, you should be good to go.
example, I worked at a culligans water plant, one of the drivers backed into my car, dented the rear 1/4 panel. he said he'd give me $100 cash not to say anything to the boss. OK so I didn't. well the guy never gave me the cash (pay you next friday thing). well then I told the boss, and he couldn't do anything since I did not report it immediately, and when asked the driver of course denied it.
since he was being "nice" about it I thought it was all good, but it was not the case.
the car the guy backed into was a $100 beater, but he didn't know that.
see how they react when you ask for it in writing that they will pay. if they start getting rude, mention how a neighbor "saw the whole thing"
anyway, good luck!