I may be buying a Dodge Stratus for cheap and the owner put a few bumper stickers on the trunk.

Anyone know of any quick ways to remove these without scratching/damaging the existing paint?

I was thinking of using a hair dryer or carefully using a heat gun to get them hot or leave in the hot sun and try to peel them using my hand.

Any tricks?

Hair dryer works great and then use some WD40 to get rid of any leftover adhesive.

They use a rubber disc made of an eraser type material on a die grinder at the body shop at work. I have also used them when removing the residue from old factory side body molding. Worked for me. These were not base coat clear coat paint jobs though. I have only heard one guy who was not too happy with them. I think 3M makes them

Hair dryer then bug and tar remover.

Penetrating oil works great. Spray it on and let it sit ten minutes. Repeat if necessary.