Anything metal is worth something at the scrap yard. As far selling, I sell quite a bit but only if it can be done without "fixing" anything. It might not sell, then you're work has been for nothing. I'll usually put something on Craig's List with a picture and if it doesn't sell with the first ad, it goes in the scrap. I've got a couple guys who come by on a regular basis just to see if I've gotten anything they want.
If you tear stuff down, mostly you want to watch for copper. In the process, you'll find aluminum, stainless steel and about anything depending on what you're tearing apart. There are several threads on this site dealing with tearing down different things.
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