Holy Cow! not to start a pissing match cause it just my opinion about my cars.
If someone came over to buy my car and had an ice pick that he was going to use to check my car ,well let's just say he better come with LOTS of money cause the price just went up 20k and at the first poke he bought the car no matter what or would pay for a COMPLETE repair. Because he just ruined the herculiner and let water/moisture an opening to get in and ruin the car. couldn't you just do like I do and reach inside the frame rails to check for weak or damaged sections. there are enough holes in the frame rails to check it all., inner wheel wells you can just push against to see if it's weak.
yeah I know you can fix it but I'd have to strip most of the sections off again to redo it(and herculiner done right is a total b#$%h to get off if done correctly),but I wouldn't have to. Since he'd have already bought it of been in court over malicious damaging a car and I'd have a professional redo it on his dime. I'd pick the most expensive resto place I could to to really nail the guy too! Magnets I can see Ice picks ahhhh not so much.