If you can show that either the dealer  in fact knew that the car had salvage title or that a reasonable dealer should have known (i.e that it would have been easy and common for a dealer to find out whether this was the case), you may be able to bring an action based in fraud--for a material (or important) misrepresentation. That could give you grounds to either rescind the transaction (return car, get money back) or to sue for monetary damages (compensation), such as the difference in value.