tips for repairing dent in door

When it oil cans, the metal is stretched. Usually you'd have to shrink the metal to eliminate that and the best, most effective way is with an oxy/acet torch but obviously this is not a paintless repair. Another option if you can find one, is an Electro-Magnetic Dent Removal System. They are very expensive though if you don't know someone who has one.
Can't hurt to try some heat with a hair dryer or paint gun, followed immediately by the dry ice. Never know, it might work and very cheap as long as you don't burn the paint with the heat gun.