When you're a scrapyard and you're shipping material out, it needs to be what you say it is. Therefore, I don't find it unreasonable to receive deductions for aluminum or any other commodity for that matter, that has other material on or in it. Basically, the deduction you receive should cover the cost of labor and time it takes to make your material "clean" so it can be sent out. There's nothing worse for a yard than having loads rejected and sent back, or receiving deductions on their end due to dirty material; that cost is generally passed on to the customer in the form of stricter rules and lower prices to compensate for the loss, standard business model really. As a rule of thumb, I give the material I turn in to my yard a "once-and-twice over" for anything that isn't supposed to be there because I like a better price, and the yard and it's workers really appreciate that.