Who is at fault when someone opens their car door and hits your car while pulling into a parking space?

It's called, "Undue care and attention" and both of you are at fault. The person didn't look to see if there was a car coming, and you didn't look to see if someone was going to open up their door. This is a "Mexican Stand-off" and it's best to come to some conclusion over this with the other person if possible ... you each share half the cost of having your vehicle being repaired. Good luck Marcy