In Iowa they have started requiring restaurants to have a trade scale that is inspected. We have to pay about $9 fee. We did have to buy a $100 scale. Our scales are inspected by the Dept of Ag in Iowa.
I checked with the State Consumer Protection and yes, whenever you sell something by weight you have to have a certified scale, pay the State a Fee and it has to be inspected annually.
In Oklahoma our scales are not inspected and their is no fee. However, we did buy a certified scale that meets the federal requirements. I forget what its called.