I understand those issues for sure, but for some reason I don't see them coming up on the Bring-a-Trailer site. It's as though buyers are convinced that BaT has thoroughly vetted every car, and that therefore most cars on BaT are essentially perfect, unless a flaw is disclosed or clearly visible in pics. Have never seen anybody ask in the comments to do a PPI, or whether one has already been done. Although, now that I think about it, it's certainly possible that bidders and the seller are communicating directly; I have seen sellers comment about bidders contacting them directly, outside the comments section. So I could envision a bidder doing a PPI and keeping the results to himself.
It seems like for GTs the biggest price factors are, in order: Heritage or not, mileage, color (the non-Heritage colors), and probably number of prior owners.
If BaT viewers / bidders are concerned about operational things like, How does it run? Does it leak? etc, I can't remember ever seen it in the auction comments.