The retailer has expert opinion
TJ this is hardly an unbiased opinion is it.
The fact that there is crash damage establishes that it is not necessarily an inherent fault and the burden of proof would return to the buyer. He would have to sue and to show that it was a manufacturing fault.
You make this sound as though there is some govt written handbook on SOGA cases?
Ultimately this will just be a squabble between two parties where the OP's mate will have to go to court if the retailer refuses to meet his expectations.
I don't know much about SOGA but I have done countless research and report writing for failure cases where my then boss did the appearing as an expert witness, and I currently provide consultancy services for a solicitors here where product failure is an issue. Admittedly I'm still learning the ropes when it comes to legalese, but my experience is that if there is obvious crash damage as described, and an expert is likely to conclude your mate bent it in a crash then this will likely only make it as far as solicitors letters if he were too push it that far. Most solicitors, upon receiving an engineers report that blames the crash will advise him to not go any further. Your mate could push it further than that but it would probably be a waste of time. Like others said, I think common sense will prevail, he is not likely to win anything because of some perceived SOGA technicality.