straightening a non-crumpled dent/distorted bumper?
 

The S4 I'm considering was lightly backed into while sitting in the driveway, it pushed in the front fender by the marker light and distorted the front bumper below where it wraps around. There are no cracks or crumple to speak of, just pushed in. Has anyone had luck straightening this sort of damage?

Is the dent where the bumper shock is? If so, it could be compressed. Replacing that may help.

try using some heat on it...heat gun on low setting- just keep moving it around the dent...so's not to heat up one spot too much...make it soft to remove the dent..and take away the dent memory

You might want to look for a PDR, paintless dent removal, guy. The have a bunch of tricks for popping out a dent without damage.