In contrast to wreckers, scrapyards typically sell everything by weight, rather than by item. To the scrapyard, the primary value of the scrap is what the smelter will give them for it, rather than the value of whatever shape the metal may be in. An auto wrecker, on the other hand, would price exactly the same scrap based on what the item does, regardless of what it weighs. Typically, if a wrecker cannot sell something above the value of the metal in it, they would then take it to the scrapyard and sell it by weight.
http://en.wikipedia.org/wiki/Scrap
http://creativecommons.org/licenses/by-sa/3.0/
http://en.wikipedia.org/wiki/Scrap
http://creativecommons.org/licenses/by-sa/3.0/