Who is at fault when someone backs into you while driving in a parking lot?

Parking Lot Accident
There are several things to consider in a parking lot accident like this one:

Where is the point-of-impact between your two vehicles? If the other car backed into your left rear door, for instance, he's probably at-fault for this loss because you have been well in control of the aisleway.
Where were your vehicles located after the impact? Was the other car half-way out of its spot? Three-quarters? Or just starting to back?
Are there any independent witnesses to confirm liability (this means anyone who was not located in your car or the other driver's car).
How wide is the parking lot aisle? If it's wide enough for two vehicles, were you traveling right next to the line of parked cars, or trying to stay in the middle in case anyone was backing?
How fast were you going?
Were the reverse lights on the other car working?
Usually, the person backing out has the greater duty to watch for oncoming traffic, but this doesn't mean negligence can't be applied to you. If you've got full coverage on your car, you might want to let your insurance company fight it out for you if the other driver's carrier doesn't accept liability.

Here are more answers and opinions from other FAQ Farmers:
Backing out of a parking lot there are two lanes one west and east. The East bound lane is for vehicles leaving the parking lot and the west lane is for enetring this parking area. There are arrow showing the flow of traffic. If vehicle A is backing out of a parking slot and barely pulls out before vehicle B stops behind him gets out stating that his car was hit. Vehicle B is now 30 inches from Vehicle A rear end in the west bound lane. Vehicle's A rear door is still inside parked slot. Now the vehicle B is now in the westbound lane heading east. There is no visual damage to Vehicle A or Vehicle B damage seems to be under the 1/4 panel on the driver side it can be felt by the hand. The driver of vehicle A believes the driver of Vehicle B to be at fault because it is in the wrong lane and this caused the collision. The driver of vehicle B maintains that anytime you are backing up, the vehicle backing up is at fault. Who has the right of way?

If you are driving in your parking lot, and someone is backing out of a parking spot.. then it's the person backing up who is at fault most likely. If he hit you from your left rear door and beyond then it's his fault. I just had an accident like this and someone backed into me. I am going to school now and going to show him the police report because he didn't write the right thing down and he wrote it was my fault, but he explained to me that day that he didn't yield, didn't look in his mirrors and so on.