The pros would probably cheekily subtitle this page, "The Do-it-yourself Approach." And it's true, while there are a lot of ways to attempt paintless dent repair on your own, and even though the various kits and tools look fairly simple, it's not nearly as easy as the infomercials would have you believe.
First, you have to pick a proper tool kit. And that's not easy for a user who has little clue what's going on. Some of them are cheap -- low prices should raise red flags. Others are so expensive (three-figures or more) that they're probably right up there with the cost of a decent professional repair (although, to be fair, if you buy the kit you can perform multiple repairs).
Many of the high-end, expensive tools are intended to be used along the inside of the panel, much like a pro would do. (Gaining access to the inside of body panels can be a chore, though, and often involves careful removal of multiple interior trim pieces.) Alternatives (which tend to be the less expensive kits) flaunt the conventional wisdom that small dents should be massaged back out from behind the painted surface. These options instruct the user to glue a tool to the dented surface and then twist or pull on the tool to pop it out. True, you can go buy the same tools as a pro, but it takes a lot of skill and experience to use them properly.
So, we've explained what the procedure looks like -- assuming it was done properly. And as you could probably guess there are a lot of ways an amateur or first-timer can get it wrong. It's different than most other car repairs because it's not about mechanical prowess; it's more about control and the ability to maintain a steady hand and a gentle pace. You can't rush it. The problem is, once a sheet metal repair starts to go awry, you're usually much, much worse off than if you'd just left it alone. Metal holds its shape, but only to a certain point.
Let's say you get a dent in the hood -- nothing too drastic, just a shallow, even dent with no sharp creases in an area that's pretty easy to reach. You think it'll be easy to pop it out on your own, so you begin to massage the underside while holding your shaping tool in place. You've made good progress so far, and a casual observer wouldn't even notice the flawed area. But it's not exactly perfect, and since it's been fairly easy to this point, you decide to keep massaging the area to make it flawless. After a few more minutes of massaging, you realize that you've pushed it just a little too far. And now you've got this flabby area on the hood where you stretched out the metal. And there's no easy way to shrink it back down. Keep going and it'll stretch even more. Lesson learned.
A good paintless dent repair might look perfect, or close to it,but the metal underneath that shiny paint is still damaged. It's thinned out and its structure has been weakened. But as long as the paint is still there and it's not immediately obvious, that's probably good enough. After all, it's not a safety concern or anything. Just remember: Sometimes it really pays to hire a pro.