[svandamme]

if they didn't cause the dent, then why should they pick up the tab for it at all?
technically , they don't even have to point it out, as you pointed out what they had to do
if they do point it out, and ask you what to do about it, then that's a courtesy to you, and then it's up to you what you want done with it: PDR by them, or hairdryer/freeze technique from youtube...