So what's the deal with weight stations?

I've stopped at a local company that sells dirt, gravel and landscaping materials both retail and wholesale. When I've needed to weigh I usually stop and walk into the office and ask. I offer to pay but they have always told me to to pull up when I was ready. They've never been so busy I had to wait, but I will let a paying customer pull onto the scales first. They usually give me a print out that looks like a cash register receipt with my weights on it.