How can I have the local salvage yard company investigated for cheating people?

I scrap metal on a daily basis. I took my scrap to the local salvage yard. They weighed it. Before I reached the counter to get paid, the weight had changed. I was cheated out of a lot of money. I asked them to research it and they showed me a picture of the previous day when I didn't have near as much scrap They would not fix the ticket. I now believe this has happened many times before. Others have complained of the same thing. I would like to have this company investigated. How do I go about it? Thank you in advance.