Toll refining for high grade like jewelry is a world of difference from scrap components. And even at 10% you are covering your acids and disposal so incoming weight charges aren't necessary.
I told him 5 to 10% would easily cover my costs, since he is dealing in large(to me) lots of karat gold. But, I also mentioned when it came to his fluffs and sweeps it would be a different rate. Solely because the amount of work, and number of processes would be greater. When i mentioned I would even recover the gold from his sink pea trap (where he washes his hands after work) as well as dust masks and papertowels that he uses to wipe his touchstone, he laughed, thinking I was joking. :shock: I assured him I was not.
But a customer bringing in components has to be told that they can have anywhere between X and Y value of precious metals in them and you want to report an accurate figure, not recover one thing and tell them something else. So they may come to grips with a fee based on incoming weight, and it may encourage them to clean the stuff up before they give it to you. Then your toll is strictly profit as long as it exceeds your expenses. But the risk is less because you know how much acid it takes per ounce and you know your disposal times and $ spent so that part should be easy to work out. Now if the scrap is a total bust and you don't recover even your expenses, you know not to take that in any more! Either way the customer never lays out cash, it all comes out of the yield.