I don't think it is the yard's way of riping someone off. The yard has worked with you for years and knows how you process your shred. This other guy may have more garbage in his loads and that is their way of compensating for it. I know that when I take stuff in to my yard, they see me pull onto the scale and know that I know where to go and what to unload where. Most the time the guys come over more to BS than to see what's in my truck. If the guy is busy working on the crane loading an outgoing truck then he will just wave and let me be. Taking in my other metals to the small scale they always look at what I have and just double check that I am getting the best price I can for what I bring in. I had a single 1LB piece of AL Siding which is .05 more than just clean AL here and he pulled it out and weighed it separate from my AL. Plus if its slow he will go through what I brought in and show me ways to get a better price and whatnot.