Rust or Not?

Pin holes in sheetmtal. The deal is it is sanded down, clean metal right, then the shop or whoever applies epoxy primer, then body filler, then blah blah ....... the porblem is that area rusted from inside of that panel to begin with and continues to rust and let moisture in under the epoxy primer and thus the filler. Filler tends to attract moisture anyway, in this case moisture from the inside of the panel, NOT the outside !
All it takes is a few pinholes and where moisture gets to it from the inside for this phenominom (spell check) too occur!!!