What's the best way to get dents out of your car?

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I finished grocery shopping yesterday and saw that some jerk had hit my car with a shopping cart (that's what happens when lazy people don't bring them back to the cart return) and there's a bit of a dent in my door. My problem is, I don't know who to call or where to go to get it fixed. A few years ago I had a dent in my car and I took it to some shady "discount" place to get it fixed and they got the dent out but screwed up my paint in the process, so I had to have that fixed a second time. What a pain. Anyway, I've moved recently, and I don't know any local places that will do it. I'd like some kind of dent removal place (like this http://www.nodents.com/ ) but there aren't any locations like that near me. Some guy at work said he "knows a guy" who could do it, but that's how I got into trouble the first time. What kind of questions or information should I get from an autobody shop before I let them try to remove my dent? Thanks!