The furthur you get your load from the center of the crane, the heavier it becomes. It's called physics.
Not to be anal here, but this is wrong. The load doesn't become heavier. The weight of the load introduces more torque the longer the arm is. Torque desribes the rotational force that will cause a system to rotate around a pivot point (in this case the crane itself or outiggers if they are out).
I agree, though. If the crane isn't rated for the load they are lifting it is likely to tip. The length of the boom arm acts as a multiplier on torque. So if they car is 100 lbs. overweight and the arm is 10 ft. long, the resulting torque is 1000 ft. lbs. The length of the arm makes a huge difference.