I've been with Dent Wizard for 24 years this summer. The process that we use is not conducive to older cars with thick sheet metal. I've been able to fix a few dents here and there over the years, but for the most part my tools bend before the dent does. If you don't believe me come on over and I'll let you look at the dings on my Dart that have been there since I bought it 12 years ago.
