Chris, you're a pro body & paint man so, in your professional view, should a correctly executed and warranted body repair not be judged to be as good as an unrepaired original panel, in which case the car's previous repair shouldn't technically have affected its value?
Personally and without being smart arsed about it I would like to think that a repair that I have undertaken could not be found by a vehicle inspector in the first place - having said that a vehicle inspector that refers to a 'professional vehicle body jig' has a 'straightening machine' is somewhat unsure of what he is taking about in the first place unless he was putting it into layman terms which could have well been the case. Having said that I fail to see how the term used that the car has been 'extremely well repaired' can be stated if he found evidence of the repair in the first place.
I do know that once metal has bent it's structure is corrupted and therefore less strong on additional impact.
All vehicle body repairers worth there salt today are fully qualified and that is not just to a collage standard either, they will have undertaken specialist accident repair training through facilities such as 'Thatcham Research' (Europe's leading vehicle body repair research & training facility for manufactures, repairers & the motor insurance sector) and based just around the corner from me. Repairers today will also fully warrant the repair undertaken
A vehicle that has been the subject of a proper impact / accident repair will be no weaker in structure than that of a undamaged identical model - equally important is the fact that the repaired vehicle will be NO stronger that the undamaged identical model - this is a critical factor due to the nature of crumple cell / zone & passenger / driver impact protection - vehicles are built to fold / collapse in certain areas and in doing so the collapsed areas absorb the energy from the impact long before it carries through into passenger / driver cell.
Should a vehicle be repaired using less welds than placed by the factory then the seams split early and the forces of impact energy fail to be absorbed or collected hence the impact energy could continue to travel further in to the passenger / driver cell than intended. Equally if a repairer goes 'gun ho' with the spot & seam welding it will also have a far reaching effect than intended upon impact - the repaired area now being over strong and instead of folding / collapsing the impact is now translated / carried into the passenger / driver cell via a structure that is far more rigid than the manufacture intended.
Like every vehicle purchaser I look for unrepaired / repaired damage - if I consider said repair well executed I would not be walking away from the vehicle - but once I had educated the vendor it would be used as leaver to reduce the price.
Now just going back to the over fabrication / over welding of repaired vehicles - I see it more times than enough but not particularly in modern vehicles - but in classics being restored - with owners / repairers often thinking that they are doing better than the factory / manufacture by welding repair areas to excess - the same principle applies - if the area is ever subject to impact the energy forces are going to travel to a greater extent than originally intended - this is a really important point to consider when taking into account the lack of impact / accident protection that is offered in classics when compared to the modern vehicle - that said I would rather see a classic repaired by over welding than the few tacks and thick application of polyester filler or worse still a bung of bridging filler with a smear of filler and some shiny paint to cover it up
1937 Jowett 8 - Project - in less pieces than the Jupiter
1943 Jowett Stationary Engine
1952 Jowett Jupiter - In lots of peices http://Jowett.org/
1952 Jowett Javelin - Largely original
1973 Rover P6 V8 - Original / 22,000 miles