With that said, why is the manufacture responsible for neglected, and or misuse of said trailer???
Just conjecture, but I don't think the manufacturer is worried about liability. If I was a manufacturer I would be PO'd at a dealer for selling one of my products when it was obviously in bad shape. I would want to know who said "it's a solid trailer". I would rather them have scrapped it then to try and re-sell it.
However, there is a possibility that the manufacturer may do something via "good-will" just to keep their name in good standing. But I agree with your line of thinking that the manufacturer should not bear any liability. But again, this is all from a layman's point of view.